Things to consider when building a cross-platform game:

1. Minimum button sizes for touch displays and small screen (eg steamdeck, mobile, nintendo switch hand held mode) is about 60 pixels. Anything smaller will fail lotcheck.
2. Visual feedback of UI interactions (Android compliance -> they'll reject a feature/showcase of your game if you don't have this).
3. Safe area/layout considerations. Avoid things like notches and app switch "chin". If you're making a game that can render edge to edge/without letter boxing. Test at an aspect ratio of 21:12 (1680x960).
4. Button input detection with keyboard, touch, and gamepad. Navigation using keyboard, gamepad, mouse.
5. Anything below 22px font size is pretty much unreadable on small screens.
6. Text fields is a world of pain on console and is delegated to the OS (think javascript alert box).
7. Scrollable/overflow UIs are extremely inaccessible to the blind and those with disabilities related to motor function.