Strange issue when connecting monitor

[Todd]

I'm running 2021.7.0 Ultimate on a new MP. Catalina 10.10.6. When I connect a small external monitor then launch Pro Tools, PT defaults to the external monitor as the audio device instead of the Apollo. When I try to switch the audio device in the Playback settings, the following error is generated every time:

Could not complete the Playback Engine command because Assertion in "/Users/autobld/gitlabci/PT/release/2021/r2/ProTools/DFW/Views/UMenu.MacOS.mm", line 1843.

I then have to quit PT and disconnect the monitor. If I start PT with the monitor disconnected, then re-connect the monitor after PT is launched, then everything works fine.

in essence, I can't launch PT with the external monitor connected.

Is there a fix for this? Thanks.