Indeed very disappointing. I tried one thing and not had crashes in past 15 days, it was crashing few times a day before that.
I need some verification from others, but I think the issue is with this setting
Settings --> Desktop and Dock --> Click wallpaper to reveal desktop --> Set this value to "Only in stage manager"
Settings --> Desktop and Dock --> Stage Manager --> Turn this off
The theory:
Clicking desktop creates this dark band around the desktop, this sends all open windows into oblivion, pushing them towards the edges out of view. I think some applications don't like being treated this way, I have had issues with Quiktime Player and also with Windows Remote Desktop, causing system crash.
To be verified: I think this issue happens when the external monitor is different aspect ratio/resolution than Mac screen. So detaching monitor might not surface the issue.
I am just another person on this forum suffering from this ill-tested feature release by apple. But since my laptop is not crashing after this setting change, I wanted to share.... and also get your feedback