I’ve used apps in fullscreen for as long as it’s been possible, and I’ve honestly never found it confusing at all.

You can move them across displays. Just open Mission Control then drag it from one screen to another. Or drag it to a desktop if you want.

As for maximising; just double click the bar at the top of the window. No extra software needed.

Now that macOS supports window tiling there’s a number of ways to lay out app windows. Fuck Stage Manager though. I’ve never been able to work out the point of it.