When I flip up the EF-X8 mount flash it does not register that flash is available i.e. I can't adjust flash settings. When I pop it back down I can adjust settings and my XT4 registers that a flash is mounted to the camera but obviously cannot take a picture with flash.    Any troubleshooting ideas?

Turn on the “shoot without lens” option: https://fujifilm-dsc.com/en-int/manual/x-t3/menu_setup/button-dial_setting/index.html p.s. Welcome to the forum.

Hello! I want to make a stenope with my XT3, so I've turn out my camera lens and put in place lens cap with a little hole. Everything is ok on the screen but the shutter release doesn't work without a lens. So how shooting?

This might help or make things worse: https://fstoppers.com/astrophotography/compare-four-ultra-wide-angle-fast-aperture-aps-c-prime-lenses-622553 I am not sure why they stuck the article in their astro section, very little of the article is about astro.

The only way I can find to make the 240P somewhat acceptable is to be in bright conditions and get the ISO as low as possible.  Do not use Flog 2!  Minimum ISO is 1250 is too high for 240P.  Flog with a minimum ISO of 640 is OK.  You even might want to consider Eterna at the lowest ISO possible. It is my impression that FujiFilm laid an egg with the stacked sensor if your goal was to shoot 240P.