MuseScore 4 does not remember its previous window size.
I use multiple screens with a very large (3849x2160) 2nd screen. However, when I start MU 4.0, the welcome always pops up on my primary (standard sized) screen, then MU 4.0 opens with a size that would fit on my primary screen. MU 3.6 handled this correctly.
I have a problem with window size in MuseScore4 as well. I use a 27" iMac and every time I start the app, it fills the entire screen. It isn't in "Full Screen Mode," it just opens a window as large as the screen. I drag the edges down to a reasonable size which is annoying to do every time I open the app. If I close the app, I have to do it all again the next time I use it.
I've searched for a solution but can find nothing. I hope this on the work list.
Of course, MuseScore4 is altogether wonderful. It's no surprise that a few issues need to be addressed.