Fret Board has question mark symbol at the nut position
S3 - Major
Ubuntu updated to rev Ubuntu 20.04.3 LTS
|LushLife G3-6LowerOctave.mscz||51.07 KB|
Wat version or MuseSore, the one from the Ubuntu repository or the AppImage?
That score stems from MuseScore 3.2.3, if that's your version you need to update to 3.6.2
Also in 3.6.2 I don't see any question marks but only proper numbers
As I recall, there was indeed a bug in this area that affected Linux only but it was fixed years ago. Update to 3.6.2 (eg, by installing the official AppImage) and it should be OK.