I too would like a mute option. I frequently have a guide track, and I’d like to hear 1) the guide track and score 2) the guide track solo 3) the score, with guide track muted.
Although at this point it’s somewhat moot for me, for a related reason: is there a way for solo to do a MIDI solo rather than mixer solo? The reason is that write mode solo simply isn’t useful with NotePerformer: I guess Dorico solos the mixer channel? So if you have two players using NP, soloing the first player still plays the second one, and soloing the second player mutes everything. The only effective way to mute / solo (that I know of) is from within NP’s dedicated mixer.
If solo meant “play only this player’s midi data” rather than “solo this player’s mixer channel” then solo would work with NotePerformer. Is that possible and I just haven’t seen it?