Well, Mike's the boss, but his response certainly contradicts
Starting in macOS Catalina, CCC offers a Full Volume Clone method in the popup menu underneath the Source selector.
Even the doc's title: "Performing a Full Volume Clone via Apple Software Restore (Beta)" doesn't make it clear, because as I said, when the option first turned up it was labeled "Full Volume Clone (Beta)" (the (Beta) since having disappeared).
OK, I tested by unchecking the "Inform me of beta releases" pref, and the Full Volume Clone option disappeared. That obviously nails it, but all the same, it's altogether unclear.
I hope Mike doesn't pull the functionality. It's not critical to me, but I like having the ability to create a bootable clone within the same container as my boot volume. Oh, well. ¯\_(ツ)_/¯
