How to remove com.apple.TimeMachine.*.backup ?

Hey, I’m on macOS Tahoe 26.2 and I suddenly ran out of space. I’ve got a 500GB drive, and in System Settings → General → Storage it shows that over 370GB is taken by “System Data”. Disk Utility also says I’ve only got about 12GB free.

Using DaisyDisk I found out that more than 110GB is taken by a single backup from over three weeks ago. To double‑check, I ran

tmutil listlocalsnapshots /

in Terminal and got:

Snapshots for disk /:
com.apple.TimeMachine.2025-12-05-210308.backup
com.apple.TimeMachine.2025-12-31-103010.local

According to DaisyDisk, that snapshot - com.apple.TimeMachine.2025-12-05-210308.backup - is the one taking up all the space.

I back up my Mac to my NAS, so I’m guessing this is some leftover from a failed snapshot, because all my other backups are on the NAS and have current timestamps. When I open the Time Machine app, I can see an old backup from December 5th, but at a different time. The 21:03 snapshot doesn’t show up there at all.

I tried:

sudo tmutil thinlocalsnapshots / 999999999999

and a restart, but nothing changed.

I also tried:

sudo tmutil deletelocalsnapshots 2025-12-05-210308

but I kept getting error"

Failed to delete local snapshot '2025-12-05-210308'
POSIXError(_nsError: Error Domain=NSPOSIXErrorDomain Code=70 "Stale NFS file handle")

Finally, in System Settings I used “Forget" for my NAS destination, deleted the whole backup from my NAS, and added the destination again. A new backup was created successfully. I hoped this would also clear the old local data, but it didn’t.

Any idea what else I can do?