Sorry this is a bit late; I didn’t think about it much because, well, everything basically works fine. There are two minor issues (you can’t see rotated movies in Usher, and menu items for saved layouts in Moom are slightly too tall), but both will be fixed in upcoming minor updates. Outside of those two things, we’re not aware of any other issues with our apps in macOS Monterey.
If you do run into a glitch of some sort, please do let us know about it.