Thanks for playing!
Unless I'm missing something, you can currently navigate all menus via keyboard only, it's just that some of them (like the inventory menu) use Q, E, TAB or space, I just need to make it clearer which menu uses which button.
Conversely, some menus you can't navigate with mouse only but that's something I'm also working on.
The ability to disembark and move on land is a planned feature, along with land combat and a basic scavenging mechanic, as I'm envisioning the game right now it's supposed to be the main way to get fuel and other supplies like food or ammo.
UI scaling and FPS limit options are now on the to-do list, thanks for suggesting them!