I play on an ultrawide 5210x2160 and prefer fullscreen mode. The game does work fine, although the UI and some other things/graphics do seem a bit oddly placed on this resolution/aspect radio, but nothing game-breaking. But, when I re-launch the game, it defaults back to windowed mode. I’m not sure if it’s also an issue with other display sizes/resolutions, but I do find it a tad annoying having to set the graphics back to fullscreen all the time. The weird thing is that sometimes (rarely!) it does remember and starts in fullscreen. It has nothing to do whether the game crashes or is exited properly - either way most of the time it reverts to windowed, but not always.
Sorry for the late reply. This is something that many have pointed out, it seems like those settings either aren’t saved correctly or are being overwritten when they should not. We’ll investigate I’ve put it on our list.