I'm curious of why I'm the first person to mention it, but if you go to settings -> video, changing the mode to "windowed" doesn't change anything, it stays fullscreen windowed. Changing the resolution doesn't actually seem to change the resolution - which makes sense in windowed fullscreen, at best the image gets slightly blurry, but it just cuts off the edges of the screen according to the aspect ratio. For example, if I change it to 1600x1200 (4:3) (native 16:9) I can only see half of the "close" button any more and left and right are black borders. I assume even if windowed mode would work, it would break in different aspect ratios.
Switching between windowed and windowed fullscreen most of the time does nothing, but sometimes freaks it out, once I had the game on both my screens.
Checking data/save/settings.xml, the setting "window mode" stays at intvalue/floatvalue = 0 and stringvalue empty, no matter which window mode I chose. Setting the string value to "windowed" just for a test did nothing, unsurprisingly.
Also, the drop down in settings -> languages is empty
Windows 10 pro, native resolution 2560x1440 144hz, two screens (game on screen 1), game version v. 0.88
And I doubt that matters, but for completeness' sake: running as administrator changes nothing, restarting the game changes nothing, graphics card is AMD ryzen 7 7800x3D, and it's not in a dir protected by the windows access control system (like c:\program files)