I got X-Plane 11 running well on Steam Deck! In fact, I even got it running along with my head tracking app SmoothTrack, thanks to an awesome X-Plane plugin...crazy stuff to have
Logitech G X52 Professional Space & Flight Simulator HOTAS Joystick
Best Joysticks For X-Plane
X-Plane 11 Tutorial: How to Configure Flight Controls and Buttons - YouTube