Some Big Sur startup volumes don't appear in the Startup Disk Preference Pane
In the past, the Startup Disk Preference Pane would list all available startup volumes, including volumes cloned by CCC (whether CCC used ASR or its own file copier). Some Big Sur cloned volumes do not appear in the Startup Disk Preference Pane, despite being perfectly bootable.
We have reported this issue to Apple (FB8889774) and we are currently awaiting a response.