I made my own mono-Downmix preset, so listening in mono already works on button press. But I’d like to check my side signal as well. There was a discussion 4-5 years ago, where you needed a 3rd party plugin to do that (or multiple stock plugins).
BTW: I am using an AHK script, which enables/disables an instance of Fabfilter Pro q 3 in the control room, which cuts away all the MID signal using a heavy low cut down to 10 Hz. But thought if there is a baked in function to do that.
I asked that 5 years ago. Internally it’s doable through second monitoring but you need separate hardware output from audio interface and some loopback(some interfaces don’t have loopback) its bit cumbersome but it works.
The way I solve it is with AHK through midi and made monitor control in melda XXX where I can solo/mute various things such as bands beside mid/solo… The benefit doing it through MXXX is that you can make signal bypassed completely untill you press one of the buttons. So for example I don’t have any crossovers until i solo some of the bands its basically in bypassed state when none of the buttons are engaged. And this only requires one midi channel in project which I have it in my template by default. In case i open some of the old project I have XML preset of that midi channel which when I imported it works right away. Also it requires LoopMIDI.
How about using a cue output? i.e. Insert a plugin with side soloed (my choice will be the voxengo msed, free and very simple, virtually no cpu cycle wasted by leaving it on all the time), take mix as a cue source and flip the monitor source by a key command?