The one thing I'm scratching my head about, and regret not having asked Mike about, is how Migration Assistant is dealing with this, and can it perhaps be used in place of CCC for some necessary functionality?
Migration Assistant only deals with the data volume. It is through the magic of firmlinks that applications installed in the data volume appear in the System volume. Quoting from Mike Bombich's Working with APFS Volume Groups
Quote
Finder shenanigans with the Applications folder
Firmlinks are mostly transparent, but there is one really noticeable exception: the Applications folder. The Applications folder at the root level of the System volume is a firmlink to the Applications folder at the root level of the Data volume, however, if you navigate to your startup disk > System > Volumes > Data > Applications, you'll notice that the bulk of the Applications are not there. Yet when you look at the Applications folder on the System volume, they are all there! The Finder applies some magic here. The read-only System Applications folder actually resides at System > Applications on the System volume, and when you open the Applications folder in the Finder, you'll see the aggregation of that folder and the Data volume's root-level Applications folder. To the average user, this is exactly what you expect to see, and that's great. However, you may notice that this same aggregation is not applied to other system volumes that your Mac is not currently booted from (e.g. your backup disk). On those volumes, if you open the root-level Applications folder on the visible System volume, you'll only see the content of the firmlink to the root-level Applications folder on the Data volume (i.e. no Apple applications, just your third-party applications and Safari). Rest assured, though, that all of the applications are backed up! You'll find them at System > Applications on the backup volume.
I'm familiar with all that, but trying to think Big Sur things through without having Big Sur as a reference point has left me at the point of pointlessness.
Note: The file path I've highlighted in red doesn't exist in Catalina, but if you follow the closest thing to it that does exist you see what Mike's talking about, although in reverse.
Mike's response to my question may be "quoted" as "Installing Big Sur on top of a CCC data clone and running Migration Assistant on top of a Big Sur installation yield the same results."
The new Great Equalizer is the SEND button.
In Memory of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire
