That 2nd monitor window thing sounds like a DPI scaling issue, especially if your main screen has different scaling than the one causing issues. I get this a lot at work because of my setup and the software I use (on windows btw) and I got so used to manually moving the window and smashing it against the top of the screen to maximize it that I don’t really mind. But maybe the term can help you troubleshoot it further
Yeah some softwares are also just bad at handling this stuff on startup I guess. Visual studio fucks up the code window’s scaling all the time for me. UE4 used to literally never open a window with the correct scaling on my second (smaller) monitor window too but it got a lot better with UE5