Mounting Big Sur volume in Catalina

I have an external ssd with Big Sur beta installed.
Booting to the external ssd works just fine - I upgraded to 20A5395g yesterday.

However, I am unable (when booted to 10.15.7) to mount the Big Sur volume.
The dialog box that presents itself reads:

Could not mount "Big Sur Boot - Data".
(com.apple.DiskManagement.disenter error -119930868)

Is this by design? Can anyone else boot a working Big Sur volume onto a Catalina system?



Mounting Big Sur volume in Catalina
 
 
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