Cautiously optimistic this is now working!! After wrestling with this for 3 days, the simple solution above of adding those 2 lines to the end of my SMB Samba extra configuration did the trick:
[Global]
fruit:metadata = stream
PLUS, it seemed to run faster, as well.
Nothing else changed… no Mac or Unraid reboot… it just worked, with several iterative backups thereafter.
My config:
Unraid V6.10.3
Monterey V12.4
Apple M1 Pro
Initial backup to dedicated share.
Thanks @UnKwicks & @Oldbean57 !!