[mahler007]

In case anyone else falls down this strange Pro Tools vortex, here's how I fixed it:

I created a new session, and chose the "Eleven" option from the IO Settings menu in the "Create New Session" dialog. Curiously, I had tried to do this several times before, but I had always been trying to apply the "Stereo" IO Settings. This would always seem to crash Pro Tools. The only thing I did differently to get it to work was choose the "Eleven" IO Settings, and I also changed the Sample Rate from 48 to 44.1.

I have no idea which of those 2 tweaks, if either, allowed it successfully create a new session with clean IO Settings. Although the settings included in the "Eleven" template were wrong, they were easy enough to fix, and the 600 dreaded, greyed out italicized "None Monitor" outputs that I couldn't previously delete had disappeared from the Output tab in the IO Settings window.

I have now successfully updated to 2021.7 and am moving forward on my ancient, 10-year old MacBook Pro...