"The selected network backup disk does not support the required capabilities."

I am seeing the above message when trying to remotely connect to a RAID5 ThunderBay 4 mini APFS volume, shared from Sharing prefs as a Time Machine volume with SoftRaid 6.2 on an Intel Mac mini. I have existing network time machine backups on this volume, so I'm pretty sure this must have been working in a prior SoftRaid version (and it's APFS so it must have been SoftRaid 6?)

The error I see in the console logs says:

com.apple.prefs.backup.remoteservice: (TimeMachine) [com.apple.TimeMachine:General] '/Volumes/ThunderBay' does not support SMB FullFSync

Is there some setting I can change on the volume that would make it support SMB FullFSync? I tried disabling write caching just in case but that didn't change anything.

If I create an APFS volume on an external USB drive and share it from the Mac mini the same way, I'm able to connect to it and use it for Time Machine remotely, so this doesn't appear to be an APFS issue.

I've even gone so far as installing Big Sur 11.6.1 on a separate volume, installed SoftRaid 6.2, exported the RAID volume for Time Machine and it still doesn't work, so this doesn't seem to be a Monterey regression...