Problems with default page size
I cannot get MuseScore to consistently use US Letter as the default page size. The instructions given in https://musescore.org/en/node/305834 DO NOT help. For one thing, the problem isn't only when importing. See details below.
Specifically, I specified US for my locale. I created a letter.mss style file by setting US Letter in page settings and then saving the score as a style. In Preferences I specified that score as the default style. For good measure I also specified it as the default style for imports.
Now if I start up MuseScore it opens with an empty score whose page size is US Letter. Good! BUT — if I use File >> New... to create a score, its page size is still A4.
If in the OS I open the printer utility, it shows US Letter as the default page size for my printer. HOWEVER, if I use File >> Print... in MuseScore and click Properties there, it shows A4 as the default page size! I don't see this behavior in any other application, but then again, the print dialog in MuseScore seems not to be the standard one, I can't find any other applications that use a print dialog like the one in MuseScore. In the dialog the other applications do use, the default page size is shown as US Letter.
OS: Linux Mint 20.2, Arch.: x86_64, MuseScore version (64-bit): 126.96.36.1997916429, revision: 1977cb3 [AppImage]