Hi again, Dr_Scardo;
I mentioned the Option-S (for me - PC - it’s Alt-S) mute ability a few days ago, in this post: In Write mode, if nothing is selected on any staff
. . . but, as this shortcut was apparently not intended to do that, it has been announced that it will be “corrected” soon, which is unfortunate.
Like you (and others), I feel that this would seem to be a basic and necessary feature, best solved by either a big “MUTE” button (in Write mode), or by making the project “Activate” button toggle with “De-activate” (which it cannot yet do).
As for being able to toggle Option-S: it is toggled by preceding it with Shift: Shift-Option-S (Shift-Alt-S, on PC).