i love this question because games are typically laser-focused on a single purpose, rather than being designed with wide compatibility as a goal. most video game ui's are so tightly integrated that there's no way to separate them from the game, but there are still some features that could be useful outside it in most games.

chording, where some action with the mouse can be combined with various keys to perform different actions, is definitely underutilised.

contextual hints, like mission markers or yelrow paint, would be very useful for beginners. likewise, contextual help like an in-game database could be expanded a lot.

hierarchical menus where a submenu is visibly on top of another is great for keeping context.

radial menus are awesome but krita is like the only non-game program i know to use it.

satisfactory lets you pin the current task to the screen, which great for not losing focus.

the concept of "blueprinting" or "maneuver planning" exists in many games but is only really available to advanced users on pc. imagine how nice it would be to set every action you wish to do beforehand so you can check the result and only commit when you like it.

autosave and rewind would be great boons for users when they mess something up.

imagine if your workspace was like a big rts map, with a little minimap in the corner to get around. you could spread things out by project, and jump to where you need.

what if you could choose a "loadout" for the day, where your hotkeys and quick tools change depending on your task?

so yeah, lots of stuff there.