Thanks sux2mfgj. I just installed beta 7, and there are some improvements: my startup disk is now correctly sealed. I tried with "toSnapshot" option on beta 7, and it's better: I can see a different error :) Validating target...done Validating source...done Couldn't set up partitions on target device - operation AddAPFSVolumeToContainer, line #5330 - error 49231 I also noticed that other vendors have the same problem. Let's hope it will be fixed for GM.

Beta 8 is better. I can finish the apfs operation: Password: Validating target...done Validating source...done Replicating ....10....20....30....40....50....60....70....80....90....100 Replicating ....10....20....30....40....50....60....70....80....90....100 Restored target device is /dev/disk3s2. Restore completed successfully. However, the result is not shown in System Preferences…     |       |   APFS Volume Disk (Role):   disk3s3 (Data)     |   Name:                      macOS Big Sur - Données (Case-insensitive)     |   Mount Point:               Not Mounted     |   Capacity Consumed:         40842784768 B (40.8 GB)     |   Sealed:                    No     |   FileVault:                 No     |     +-> Volume disk3s2 B47FE0AC-CD4C-4444-BE16-785C96F6EFD5     |       |   APFS Volume Disk (Role):   disk3s2 (System)     |   Name:                      macOS Big Sur (Case-insensitive)     |   Mount Point:               Not Mounted     |   Capacity Consumed:         15706312704 B (15.7 GB)     |   Sealed:                    Broken     |   FileVault:                 No     |     +-> Volume disk3s4 72F5627F-D60D-40A7-B1C9-CED3A8BD80E3     |       |   APFS Volume Disk (Role):   disk3s4 (Preboot)     |   Name:                      Preboot (Case-insensitive)     |   Mount Point:               Not Mounted     |   Capacity Consumed:         528404480 B (528.4 MB)     |   Sealed:                    No     |   FileVault:                 No     |     +-> Volume disk3s5 29D5A484-E049-4239-8D4C-8ECDBEED7B67                 APFS Volume Disk (Role):   disk3s5 (Recovery)         Name:                      Recovery (Case-insensitive)         Mount Point:               Not Mounted         Capacity Consumed:         765935616 B (765.9 MB)         Sealed:                    No         FileVault:                 No

In beta 9, asr did almost work. By almost, I mean that the command succeeded, but the resulting volume is still not bootable. But there is a regression in beta 10 : the command failed. I tried several options, but it's ending on a failure on: "Couldn't embed the APFS EFI driver - erreur 49174" I hope this is not the GM…