It appears that creating a bootable clone of Big Sur (macOS 11) will not be possible unless and until Apple creates a revised APFS replication utility. Apparently the "Copy All Files" and "Copy Some Files" options of old will no longer work for system files and volumes. This just in from today's beta release of Carbon Copy Cloner.
Originally Posted by Mike Bobbich (CCC Developer)
We're wrapping up our beta testing cycle for macOS "Big Sur" 11. CCC will create Data Volume backups of any Big Sur startup volumes. Apple's APFS replication utility is still not currently capable of replicating a Big Sur System volume (as of Big Sur Beta 8). We're working with Apple to develop the functionality within macOS that will allow third-party backup applications to continue making backups of macOS System volumes. In the meantime, we're making complete backups of your data, and those backups can be seamlessly used alongside the macOS Installer or Migration Assistant to produce a bootable backup or to facilitate a restore
