Clone/backup computer with Disk Utility in Big Sur

Actually, it is really easy to use; I've been using it for many years. You can - but do not have to - use advanced features. You can simply do a simple full clone without needing to set up anything. Or you can set it up and have it do things automatically. I actually prefer the manual method.

I am unable to answer your question re. DU; however, the only backup I've heard of that works with Big Sur at this point is Time machine. I am waiting for CarbonCopyCloner and SuperDuper to get the problems worked out.

The seal has to do with the new way, adopted in macOS 11 (Big Sur) in which Apple encrypts the System - and so adds security by making its files inaccessible to users.

This has to do with the advances in the Apple Filing System (APFS). Carbon Copy Cloner works well on APFS volumes up to and including 11.1

Suggest using that. Good luck :-)

You can use Carbon Copy Cloner latest release.. I have used it and no issues. Just be sure to follow the process. If you have a new M1 Mac then the process is in two steps: 1) Copy data vol to drive and 2) use recovery to install Big Sur on the drive and you are all set.