Installing Big Sur on External drive

Is there a trick to successfully installing macOS Big Sur on an ext. drive and the drive not getting corrupted when switching back to Catalina on the internal drive? I understand the issue (64411484), about being on the same APFS container, but don't the internal and external drives each have their own container?

Everything is fine until I try to switch over to Catalina, either on a T2 Mac or a non-T2 Mac. Then the entire Big Sur volume is corrupted. Are there more explicit install instructions available from Apple given the known bugs?

I would really like to be able to have a stable setup that isn't corrupted each time I need to switch back to Catalina.

Any tips or suggestions are appreciated.
Installing Big Sur on External drive
 
 
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