Why are these files created since installing Tahoe 26.1?

The files are created by Time Machine. TM will create and store a local snapshot hourly for the last 24 hours plus the last complete backup for each TM destination that wasn't connected in the last 24 hours. Those are in addition to the backups written to the destination disk(s). TM does this for quick access to the backups (and so you have some backups even if the destination disk is not available). You can see that if you use the TM browser because the snapshots are available immediately, then if available the backup source is added.

The way to delete local TM snapshots (if you feel you must) is in Disk Utility. Select the Data volume in the sidebar (or the volume group, the right under the container disk) then select View menu > Show APFS Snapshots.

With that, you will see the snapshots listed.

You can select one or more and click the (–) button at the bottom to delete them. If you select them all and let DU calculate, it will show the summary 'private size' at the bottom, that's the total utilization of space for snapshots (it's not the sum of the individual sizes). Is that where you are getting the '80 GB lost' value? I ask because I don't see that usage anywhere in your screenshots.

You can delete them, but TM will just recreate them so the regained space is only temporary.

As colleagues have pointed out, you may need to reconnect the NAS as a TM backup to be able to get around the "Stale NFS file handle" error. Assuming you haven't erased the backups on the Synology NAS, if you select it as a TM destination you should be prompted to Claim the Backups, and you should choose that option.

Bigger picture, personally I have no issues with TM backups to a Synology DS223j. Five Macs in the house back up to it, and I also have a set of 4 TB SSDs that I use as secondary backups and connect once a week to run a backup then swap the SSDs to an office location (that's why my list of snapshots in the screenshot above has one from 11/11 and 11/18, those are the last successful backups to the SSDs and the others starring with 'yesterday' are the past 24 hours that are also backing up to the NAS).

Here is an Apple article with instructions to view & delete APFS snapshots. You must first enable the "View --> Show APFS Snapshots...." option while you have the "Data" volume selecting within Disk Utility:

View APFS snapshots in Disk Utility on Mac - Apple Support

FYI, the other day someone else was trying to delete APFS snapshot using the command line & was unsuccessful, but succeeded when using Disk Utility.

As for using TM with a NAS, you must be using SMB and making sure only ASCII characters are used in the name of the share. AFP networking is no longer supported.

You may need to make sure your NAS is completely up to date for its OS and firmware & is properly configured. You may need to contact Synology support if you still encounter issues.

This is above my pay grade

From what I have read elsewhere

When Time Machine can’t reach the network backup destination (your DS215j) or when the destination returns stale metadata, macOS creates local snapshots so it can still preserve rollback points.

" Failed to delete local snapshot '2025-11-17-031807'

POSIXError(_nsError: Error Domain=NSPOSIXErrorDomain Code=70 "Stale NFS file handle") "

means the APFS snapshot record exists, but the underlying data cannot resolve because the metadata references a file handle that Time Machine recorded when talking to the network drive.

In short: The snapshot is corrupted / orphaned.

You won’t be able to delete it with regular tmutil commands.

How to fix this is where I am sorry to say - I do not know how

You are welcome

I am aware there are several Other Contributors who use NAS for Time Machine Backups

Perhaps 1 or more may chip in on your question and offer a safe solution

For me and me alone

I tend to think NAS backups are ok sort of

Not suggesting you alter your setup

But NAS backups are only reliable when they are reliable and are dependent on a reliable and fast Internet Connection

Not always the case when the backup is required and usually when an Internet Connection is not available

Even the maker of Carbon Copy Cloner tends to shy away from using this type of a setup

Not compatible with Migration Assistant, no backup versioning

There. my friend

One of several persons who use a NAS Setup has appeared and hope this may solve the issue 🤞

🦉-53

Try using Disk Utility to delete the snapshot.

Select the Data volume, and it will show you the existing Time Machine snapshots.

Select that one and press delete (or click the "-" button). What happens?

Follow the previous advise - First

Though, must ask

When was the last time you ran Time Machine

" 80GB lost " due to Time Machine Snapshots seems excessive like about 7 - 8 Days of not running TM Backup

I use a different way to backup - Carbon Copy Cloner and do a manual backup once a day

From the screen shot below

Each days backup ranges from about 1.14 GB up to 2.04 GB

Tested using a M4 Mac Mini with macOS 26.1 Tahoe

The "View->Show APFS Snapshots" is only available when you have the Data volume selected.

If it is dimmed, it is presumably because you have another volume or device selected.