Last week I tried to give MuseScore 4 a chance to test Muse Sounds, and unfortunately it was a disaster...
I have the same concerns as others about the closed source nature of Muse Hub, which is shared by others in their community too apparently, but I was curious so I decided to try and use it anyway. Not sure why it needed root access just to download stuff, but eventually it downloaded the 14GB of sounds for all orchestra sections (it always crashed any time I tried the integrated audio snippet preview, though). That said, MuseScore 4 never found the sounds when I tried to configure them: tried the Flatpak version and it couldn't detect them; tried the AppImage version (that some said would work with Sounds, unlike the Flatpak) and that didn't work either. To make things worse, it looks like M4 doesn't have any setting to disable telemetry as M3 did, but again, I wanted to give Sounds a chance so I was willing to try it anyway.
As a result, I just deleted everything, and I'm still on M3. I guess it's just not ready to work on anything they didn't specifically targeted the code for (Ubuntu probably, while I'm on Fedora), which unfortunately does indeed sound much more like what closed software usually does, than what you'd expect from open source. Not sure if M4 will eventually land in Fedora's repos (Hub won't since it is and remains closed), maybe I'll give it a try again when that happens.