"MuseScore File" string (under File -> Save As...) does not indicate which version you are about to save as
There is no indiation that the file you are about to save, is saving version 3 format (on MS3), or version 2 format (on MS2). This is dangerous, especially when opening a V2 file in MS3 and hoping to keep the ability to edit the .MSCZ file in MS2.
What would make it more transparent, is to change the string in Transifex
from MuseScore File
to MuseScore 3 File
I do not regard the following as very good arguments for the current behaviour
a) It has always been like that. It was the same when transitioning from V1 to V2. (Counter argument: this is just repeating the same mistake)
b) The user is using MuseScore 3. They should know that they are saving in a MuseScore 3 specific format.
but you are welcome to try and convince me otherwise.
ps: I don't know if there are other places where an explicit version number would make sense.