Doug Pardee

Color filters are normally used with B&W film. Your X-T4 already has yellow, green, and red filter options for the in-camera B&W (and Acros) film simulations.
If you're post-processing into B&W, just about all B&W conversion software provides color filtering capabilities.

The news is not good. See this earlier thread:
 

1. DxO refuses to have anything to do with X-Trans sensors. Until very recently, they refused to have anything to do with Fujifilm at all, even their Bayer-sensored cameras.
2. Fujifilm -- along with Olympus, Panasonic, and Ricoh/Pentax -- honors the traditional "18% gray" brightness target value. That brightness goal was set during the days of B&W photography, and we've learned that color photographs tend to look a bit "underexposed" at that brightness level. For that reason, Canon's DSLRs derate the ISO number, so that you get about one stop brighter image -- about 35% gray. Sony does the same, and Nikon changed over about a decade back. So the "Big 3" manufacturers all use an ISO rating system that produces images about a stop brighter than those produced by Fuji/Oly/Panny/Pentax.
What is measured as ISO 200 on the old "18% gray" plan is now being marked as ISO 100 by the big brands. In fact, when NIkon made the change, people commented about how Nikon DSLRs used to only go down to ISO 200 but now were going down to ISO 100. To get 18% gray on one of the big guy's cameras, you need to meter at twice the ISO that the camera is set to. [By the way, Canon tried the 18% gray target in the Rebel XTi/400D DSLR, and people complained about how dark its pictures were.]
When using in-camera metering on Fuji, the multi-zone metering runs about a stop brighter than the "dumb" metering modes. That way Fuji produces the same bright color images that the Big 3 manufacturers do -- in Multi metering mode. But the difference in brightness between in-camera metering modes catches a lot of people off-guard.
Personal opinion: the days of "18% gray" are behind us. Canon, Nikon, and Sony have long abandoned that standard, and virtually nobody has complained. It's probably time for Fuji/Oly/Panny/Pentax to make the change, too.

1. DxO refuses to have anything to do with X-Trans sensors. Until very recently, they refused to have anything to do with Fujifilm at all, even their Bayer-sensored cameras.
2. Fujifilm -- along with Olympus, Panasonic, and Ricoh/Pentax -- honors the traditional "18% gray" brightness target value. That brightness goal was set during the days of B&W photography, and we've learned that color photographs tend to look a bit "underexposed" at that brightness level. For that reason, Canon's DSLRs derate the ISO number, so that you get about one stop brighter image -- about 35% gray. Sony does the same, and Nikon changed over about a decade back. So the "Big 3" manufacturers all use an ISO rating system that produces images about a stop brighter than those produced by Fuji/Oly/Panny/Pentax.
What is measured as ISO 200 on the old "18% gray" plan is now being marked as ISO 100 by the big brands. In fact, when NIkon made the change, people commented about how Nikon DSLRs used to only go down to ISO 200 but now were going down to ISO 100. To get 18% gray on one of the big guy's cameras, you need to meter at twice the ISO that the camera is set to. [By the way, Canon tried the 18% gray target in the Rebel XTi/400D DSLR, and people complained about how dark its pictures were.]
When using in-camera metering on Fuji, the multi-zone metering runs about a stop brighter than the "dumb" metering modes. That way Fuji produces the same bright color images that the Big 3 manufacturers do -- in Multi metering mode. But the difference in brightness between in-camera metering modes catches a lot of people off-guard.
Personal opinion: the days of "18% gray" are behind us. Canon, Nikon, and Sony have long abandoned that standard, and virtually nobody has complained. It's probably time for Fuji/Oly/Panny/Pentax to make the change, too.

Film simulation is just one piece of a Custom Setting. When you select a Custom Setting, you are loading the entire Custom Setting into the camera. All of the many parts of that Custom Setting --- film simulation, white balance, highlight tones, shadow tones, color saturation, noise reduction, sharpening, DR, etc. -- will replace whatever your camera had been set to. When you change the film simulation, that changes just the film simulation, without changing anything else.
You just need to set up a "standard" Custom Setting. It's probably most convenient to put that in C1.

The 35 f/2 should be reasonably quiet.
All Fujifilm lenses faster than f/2, and that includes your 23mm and 56mm, have to move a lot of glass to change focus. That requires powerful AF motors which are slow and noisy.
The quietest lenses are those with linear motors, which you can easily recognize by the LM in their official designation. At the moment, most of those are zooms. The XF90mmF2 R LM WR is the only LM prime I know of, although it does require four linear motors to shove its focusing glass around.

Which AF Mode are you using? (Go into the menu and look at the first screen of AF/MF setting).
It might help if you read the tutorial at this link which explains how the camera focuses and the effect of the different modes.
https://fujifilm-x.com/af/en/af_mode/
It was written before the X-T3 and X-T30 but the principle is the same - the main difference is that phase detection now works across the entire screen. 
 

There is a difference between Film Simulation and Custom Profile - changing the Film Simulation doesn't automatically change the Custom Profile.
If you want the different settings for different Film Simulations then set up different Custom Profiles.

M3:2 reduces resolution to 12 megapixels. For highest quality, you should use L3:2 to get 24 megapixels.
That said, 12 megapixels would normally produce JPEGs somewhere in the neighborhood of 5 megabytes.
So I'm wondering if you're looking at those files on your mobile phone, after transferring them from your camera using the app. If so, you probably have the Resize for Smartphone option turned on, which transmits only 3 megapixels to the phone. If that's the case, the files on the SD card will still be full-sized.

You're probably messing with Custom Settings, perhaps via the Q menu.
This is all very confusing, so you may need to go through this explanation a few times.
On models without an ISO dial (like your X-T30), each Custom Setting (C1-C7) has a full set of auto-ISO parameters for all 3 auto-ISOs, plus a selection for which ISO to use. Which may or may not be one of the auto-ISO choices.
Every time that you select a Custom Setting, the auto-ISO parameters for that Custom Setting completely overwrite the auto-ISO parameters in the camera.
When you open the Q menu, the "cursor" is often set at the Custom Setting selector box. If you then move the rear command dial (perhaps in a misguided attempt to move to a different selector box, something I would never do 😏), you activate a new Custom Setting. Unless you notice this and return the Custom Setting selector to BASE before exiting the Q menu, when you exit the Q menu the auto-ISO parameters for the selected Custom Setting will overwrite the ones in the camera.
How I deal with that is easy to understand but a pain to set up initially: I set the auto-ISO parameters in all 7 Custom Settings to the same thing. This can take a while. If you don't use the Custom Settings -- or are prepared to reconfigure them -- you can set the camera auto-ISO to whatever you want, then go into the Edit/Save Custom Setting menu item and, for each of the 7 Custom Settings, choose "Save Current Settings". That will completely overwrite that Custom Setting with however the camera is currently set up, and is a lot faster than going into each Custom Setting and setting up 9 auto-ISO parameters on each one.
Regardless, the basic rule for models without an ISO dial is that the auto-ISO configuration being used by the camera is essentially temporary, and will be overwritten any time a Custom Setting is selected.

Most likely you've set up your touchscreen to select the focus point and bump your nose against it while framing!😀

The use of DR-Auto, DR200, and DR400 can raise the minimum ISO allowed. The 16-megapixel models can only do ISO 100 in JPEG mode, not in Raw or Raw+JPEG. Lens clutch set to manual-focus mode (for the lens models with a clutch). Manual-focus lens fitted.

The use of DR-Auto, DR200, and DR400 can raise the minimum ISO allowed. The 16-megapixel models can only do ISO 100 in JPEG mode, not in Raw or Raw+JPEG. Lens clutch set to manual-focus mode (for the lens models with a clutch). Manual-focus lens fitted.

Try to press the (rear) dial, you should be able to change the exposure time then. 

Probably this - or maybe touch focus
You might try turning off touch focus and face detection - then set focus to single point and touch the joystick once to centre the focus point.

Don't confuse the two things.
Custom Settings C1-C7 allow you to set up virtual film types for JPEG shooting.
The Q Menu is a control panel that allow you to see and to change 16 different camera settings of your choice. Unlike function buttons, the Q Menu shows the current setting as well as allowing you to change the setting. There is only one Q Menu. It is the Q Menu.
As shipped by the factory, one of the settings in the Q Menu is the Custom Setting. That's the only connection between the two, but somehow people manage to get them confused all the time.

The custom settings are essentially "virtual film types" for JPEG shooters. Raw shooters will have no use for custom settings. [On the cameras that don't have ISO dials -- X-T10/20/30 and X-E2/2S/3 -- the custom settings include ISO settings and, more importantly, auto-ISO configurations. Some Raw shooters might find having multiple auto-ISO configurations useful.]
Because the Fuji uses control knobs for many functions, and there's no notion of PASM modes, exposure controls can't be saved and restored by the camera. This is, to me, the big downside of the direct controls.
It would be nice if Fuji would at least let you set up a number of autofocus configurations. They couldn't control AF-S vs. AF-C, but all of the other AF settings are "soft."
The Q menu is something totally different. It's a control panel that you can bring up with a single button-push that shows how 16 different features are currently configured, and allows you to change their settings directly from that control panel. You get to choose which features appear in the panel and how it's laid out. The Q menu doesn't "save" anything for later -- it changes the current camera settings.

Just FYI: the usual term for that is "brassing." Yeah, that's not all that helpful.

The problem (at least for me) has always been to get my head around the fact that the Q Menu and the Custom Settings are different concepts.
Just because you can see some of the Custom Settings in the Q Menu does not mean they are the same thing.

Is this X-T2? Are you shooting in raw (or raw + jpg on separate cards)?
In order to zoom in further the camera needs the fine jpg.
Shoot raw + fine jpg on the same card (or use separate cards and switch to the jpg when you preview)

My Yongnuo triggers work on my X-T10, so you should be able to make it work.
Can you tell us what your flash settings are in your camera? The X-T2 has a far more extensive flash set-up than my simple X-T10 does. As a "check that it's plugged in" example, do you have "Flash Control Mode" set to M?
You might want to review this page:
http://fujifilm-dsc.com/en/manual/x-t2_v41/peripherals_and_options/external_flash_units/index.html

Select any Auto scene mode other than SR+ -- use Portrait, Portrait Enhancer, Landscape, Sport, etc.
SR+ (automated scene recognition) needs to continuously scan to determine what kind of scene the camera is pointed at now. That includes varying the focus. If you leave the camera pointed at a scene for a few seconds, SR+ should settle down. As soon as you point somewhere else, or something in the scene changes, it'll start back up again.
If you select a specific scene mode, there's no need for all of that scanning.
SR+ is a battery hog, and if you're going to use Auto, I definitely recommend selecting an appropriate scene mode whenever you can.
Oh, and the lens difference is just that the 27mm focuses by moving the entire optical assembly back and forth, which is slow and noisy... but retains excellent IQ given the restrictions of the pancake form factor. You'll see similar behavior on the Fuji primes that are faster than f/2. The 16-50 was doing the same thing, but with its lightweight inner-focusing system it's only obvious if you're looking through the viewfinder.

Have you tried Lossless Compressed under IQ=>Raw Recording in the menu?

I don't know exactly how that camera handles back-button AF-C with AF-M -- the X-T2 has a separate "Shutter AF" option for disengaging AF from the shutter release and my X-T10 doesn't -- so I can't help you there. I'd assume, however, that it's normal -- the camera's just waiting for the lens to finish focusing.
 
I personally don't recommend back-button AF-C for general use. If you really need AF-C, then you need it. But if you've got it set to AF-C just in case someday you want AF-C, be aware that if your shooting aperture is at f/9 or higher, the camera will not use phase-detect AF. If you're controlling the aperture, it's usually easy enough to avoid that issue. But if you're shooting P mode, in daylight the camera might select f/9 or higher, leaving you with unnecessarily slow contrast-detect AF.
 
Fujifilm doesn't publish most of this stuff. That's why there are so many third-party books, such as Rico Pfirstinger's that are advertised on this site. Pfirstinger, for example, recommends skipping AF-C for simple tracking AF when you're only going to take one shot. He recommends using AF-S and "mashing" the shutter button down in one stroke, skipping the half-press. That way, as soon as the lens has focused, the shutter is released. That should give AF results as accurate as AF-C.
 
And yes, in single-point AF, the camera will try CDAF if PDAF fails, regardless of which PDAF point you select. Unless you're in AF-C with CH drive, in which case the camera uses only PDAF at apertures of f/8 or below, and only CDAF at apertures of f/9 or above.

That's what Fujifilm's Release Priority does. Fuji will never take a picture while focusing is still in progress -- it always waits for focus to complete. The Release Priority tells it that if the focus completes as a "failure" (!AF would display in the viewfinder) to go ahead and take a picture anyway.
 
With contrast-detect autofocus (CDAF), that's probably a wasted shot, because you don't know where contrast detect will leave the focus when the camera gives up and declares failure. With phase-detect autofocus (PDAF), the lens probably never changed focus, and that's more likely to be usable -- especially during burst shooting.
 
Note that with single-point AF, a PDAF failure will result in the camera switching to CDAF and trying that, so Release Priority rarely will give a usable picture with failed single-point AF. Big exception: single-point AF (on a PDAF point of course) with AF-C and CH and aperture of f/8 or wider will never try CDAF even if PDAF fails -- again, we're talking about a burst shooting setup. If you use single-point AF and sometimes do burst shooting, my personal recommendation is to set Focus Priority for AF-S and Release Priority for AF-C.
 
PDAF failure is close to instantaneous. It sounds like you're experiencing CDAF failure -- either because you're using a configuration that only uses CDAF, or more likely you're using single-point PDAF and the camera is trying CDAF when PDAF fails.