I had the same problem, also Ubuntu 20.04 and Samba 4.11.6 My backup machine is on btrfs and not on zfs, but ScruffyDans solution put me on the right track I think (still testing). I modified my smb.conf to include as global options: fruit:nfs_aces = no inherit permissions = yes I got it from here: https://stackoverflow.com/questions/58496277/samba-4-10-server-config-using-module-vfs-fruit-changes-file-creation-mask-fo Changing these settings allowed my MacBook Pro with Big Sur to connect to a network share, create a new .sparsebundle and it is now backing up to it. I can also confirm that the container created in the .sparsebundle is an APFS container! Before changing these settings it would just throw the error as described in the OP. I'm not sure why this seems to solve the problem....anyone?