If you change the 1Password pop-up menu shortcut from "Cmd+\" to anything else, then try to set it back or press the "restore old shortcut" icon, you get an alert that it conflicts with a system shortcut. I checked all of my system shortcuts in my system preferences and nothing comes up.
1Password Version: Not Provided
Extension Version: Not Provided
OS Version: macOS Monterey Public Beta
Sync Type: Not Provided