TimeMachine support for Big Sur - missing F_FULLFSYNC?

[Tom Talpey]

I've installed Big Sur on one of my Macs and am trying to configure
Time Machine over SMB to my Ubuntu 18.04 server, running Samba 4.7.6.
The share works fine, but TM refuses to use it. Upon inspecting the
TM client log, I find it spews:

 > Big Sur
> 2021-03-01 21:16:54  '/Volumes/TimeMachine' does not support SMB FullFSync
> 2021-03-01 21:16:54  '/Volumes/TimeMachine' not offered as a Time Machine destination because it does not have the correct capabilities.

Does the 4.7.6 version of vfs_fruit support F_FULLFSYNC advertisement?
I find some mentions of earlier versions supporting F_FULLSYNC (no extra
"F"!), but zero mention of either fullsync or fullfsync in release notes
for any Samba/vfs_fruit version. Is that just a typo, in which case, why
is Big Sur complaining?

Apologies for posting to samba-technical if this is inappropriate here,
but thanks for any enlightenment!

Tom.