3.1 Beta+nightly: Feature or bug that only the marked staff is played?
Of course, it's not bad to be able to play only one staff/voice without much effort (instead of using the mixer, for example). But most people will use the possibility to click on a measure to start playing from that point, to hear all staffs/voices.
In 3.1 Beta/nightly you unfortunately have to mark the measure, from which you want to play, in all staffs.
In a really large symphonic score with many voices, the whole thing quickly becomes very uncomfortable. If the whole thing is not a bug and you want this functionality, then an additional symbol in the menu bar would be better. In Capella (=popular music notation program in Germany) they did it that way:
The speaker symbol corresponds to the Play button ▶ in MuseScore. The single speaker plays only the selected staff, the double speaker plays all staffs.
OS: Windows 10 (10.0), Arch.: x86_64, MuseScore version (64-bit): 18.104.22.16807, revision: 60546fc