In Things 3 (free trial available at their website) a particular dropdown menu doesn't work with Yabai (SIP enabled) and the problem may appear elsewhere.
To reproduce this error, go to File > New Repeating To Do. An overlaid window appears:

The two dropdown menus (currently 'after completion' and 'week') hide a fraction of a second after I click on them and I can't interact with them using the keyboard either.
I've run into similar issues in other applications, including the Hot Corners popup within macOS System Preferences > Desktop & Screen Saver > Hot Corners:

Seems like this is an issue when window_topmost setting is enabled, yeah?
For me this bug was omnipresent in Big Sur. After reading this and disabling window_topmost dropdowns are behaving normally again.
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For me this bug was omnipresent in Big Sur. After reading this and disabling
window_topmostdropdowns are behaving normally again.