Ah, that's probably what it is then - I'm using a slow exposure and no flash. I just have the 1st and 3rd options on my menu. I bought a mirrorless camera because I thought it would be better than my dslrs but it's pretty useless for what I wanted it for. No live view/tethering And can't even use the electronic shutter Yet I can take a 4k video. It doesn't make sense that I can do that but can't take a still.
That is odd, there are very few other settings that limit using es. Having a flash unit attached is one, but I would have thought that would also keep you from using ms+es.
Mines does this:
Have you upgraded to the most recent firmware?
This may sound drastic, have you copied you settings down somewhere and tried a full reset?
I agree with all that's been said above, hence my decision to buy XS10 rather than XT4. The reputation of Pentax was that if it got covered in mud you could wash it under a running tap. I never tried that but was happy to use it in briefly in heavy rain and desert sandstorms and never had a problem. I wouldn't be that confident in such circumstances without weather sealing and would use poly bag and chamois even in less extreme conditions.
It's often the small doors covering SD slots, batteries etc that aren't sealed, and some times cable and microphone or remote shutter sockets have no cover at all. Sealing a pop-up flash isn't easy either. Worth protecting those points if you're out in weather you want to protect yourself from.
Scroll down to Shutter Type.
It is in the shooting menus setup, you can choose between manual shutter, electronic shutter or both together.