When searching for new apps by Title or Category the Musescore App does NOT appear in the lists. However, I do have it installed on some of my portable drives and it has been updating somewhat recently. I can also find it on the website and can download it.
Is there some reason for omitting what I'm thinking is a normal and legitimate app from said lists?
Do you have it installed but hidden? (right-click any other app and select Show Hidden to see) The current version is offered to Windows 10 x64/11 users and the legacy 3.6.2 is offered to Windows 7/8/8.1 and 10 32-bit users in the platform by default.
Sometimes, the impossible can become possible, if you're awesome!