System is current Goldeneye and the Time Machine’s SMB share has set its purpose to “Time Machine Share”. Other Macs happily backup there although their sparsebundles were created before macOS Tahoe.
Now there’s a new Macbook Pro with Tahoe that I try to setup. When setting the Time Machine to the around 10 seconds and you up end up with an empty directory on the share named “machine name 2025-12-07-160742.incomplete”.
This is the ticket tracking the actual fix (which is pulling in latest Samba minor release). In this case we had a fairly constant trickle of tickets filed by community members that are being closed as duplicates.