i raised that FR in Rsync Task should allow local 2 local synchronisation ( Local Destination Target ) - Feature Requests - TrueNAS Community Forums
But your comment gave me the correct idea. I’ve mounted the SAMBA Share via CLI and will do rsync test
truenas_admin@truenas[~]$sudo mount -t cifs -o username=‘user’,password=‘password’,domain=WORKGROUP //192.168.178.56/TN-Sync-4TB /mnt/smb
truenas_admin@truenas[~]$ sudo rsync -rh /mnt/WD8TB/BACKUP /mnt/smb --ignore-existing --delete --info=progress2
227.10M 1% 1.05GB/s 0:00:00 (xfr#1, ir-chk=1058/1082)