How to fix when Mac Studio internal drive storage is full

Most likely the "deleted" files are still on the drive in a hidden APFS backup snapshot. Until the APFS snapshot backup is transferred to the backup drive, the APFS snapshot will remain. It may even remain until the next backup snapshot is made before it will be deleted. Eventually the APFS snapshot will be automatically deleted along with the backup copy of the 1.3TB of data you just deleted.

With some backup apps, you can configure snapshot behavior. I have no idea what options are available if using Time Machine.

You can view APFS snapshots by using the instructions in this Apple article:

View APFS snapshots in Disk Utility on Mac - Apple Support

Make sure to have selected the "Data" volume on the left pane of Disk Utility first so that the "Show APFS Snapshots" option becomes available on the Disk Utility View menu on the menu bar.

I would not delete the APFS snapshot unless you are certain its contents have already been fully transferred to the backup drive.

<< The behavior the OP described sure sounds like the system adjusting the storage numbers from data to snapshot (system). >>

I agree.

But the approved method for releasing Time machine snapshots is to let your Time machine backup process RUN, and it's been days now.

This article suggest that Disk Utility can see and list snapshots for you. (Ventura and later).

choose View > Show APFS Snapshots.

Select a Volume

View APFS snapshots in Disk Utility on Mac - Apple Support

it also suggests you may be able to select and delete one, but I remain skeptical of time machine items of any kind.

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Grant Bennet-Alder wrote:

But the approved method for releasing Time machine snapshots is to let your Time machine backup process RUN, and it's been days now.

Main thing is to confirm this is the problem.

it also suggests you may be able to select and delete one, but I remain skeptical of time machine items of any kind..

I definitely do not like the idea of deleting TM snapshots without knowing if they have already been transferred to external media. Is there any way to confirm this? Does TM have any logs of its activity to confirm a successful transfer? I don't use TM, neither does my organization.

And are there any TM settings to retain snapshots on the local drive? I have heard other backup apps do have options for configuring snapshot retention.

I doubt deleting a local TM snapshot will hurt TM itself unless the data within the snapshot has only been partially transferred. I would be concerned about losing a backup of other modified documents within that snapshot(s) which may be important if they have not yet been transferred to the external drive. However, if the TM snapshot still has not been automatically deleted, then something is going on with the backups.

While writing this, I wonder if the OP should boot into Safe Mode and let the Mac sit there for a while to see if the backups are transferred and the TM snapshots are automatically deleted. Maybe even a simple reboot would even be enough.

<< I need the operating system to function properly. >>

That would certainly be nice, but I know of no magic buttons that can be pushed to make that happen. MacOS is the product of hundreds of thousands of person-years of effort to create it, and its internal complexity can be daunting.

Instead, I just reach for whatever handles I can reach. Identifying what file or files are hogging all your extra space seems like it could lead to a solution to your issues.

the root cause is that you do not have your Time machine DRIVE connected, so Time machine builds a LOCAL snapshot of files to be backed up, and waits until you connect the drive to unload that snapshot onto the backup drive.

When you come along and say delete dozens of files, your space may be not immediately returned because 'copies' of dozens of files are included in the snapshot, still waiting to be saved to disk.

adjusting the exclude list may provide long term improvement, but may not provide immediate relief.

Connecting your drive more often and letting Time machine run will releve this sort of constipation more quickly.

then the idea that these files remain in snapshot files is not very credible.

Readers look forward to you running any one of the suggested Utilities that can IDENTIFY, but do not actively DELETE the largest files.

Grant Bennet-Alder wrote:

then the idea that these files remain in snapshot files is not very credible.

Readers look forward to you running any one of the suggested Utilities that can IDENTIFY, but do not actively DELETE the largest files.

If the 1.3TB still has not been released, I would still first check to see if there are any outstanding APFS snapshots still remaining from the day the OP was deleting the 1.3TB of data (and earlier). The behavior the OP described sure sounds like the system adjusting the storage numbers from data to snapshot (system). I've seen some posts on this forum where a person had several TM snapshots. It is possible TM may be a bit slow on its maintenance or has gotten stuck even though the backup drive is always connected.

APFS snapshots won't show up in the storage apps.

consider using one of the Utilities mentioned in this article to find out what files are the biggest:

What is “Other” storage on a Mac, and how… - Apple Community

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<< There's a huge system data file that I can't do anything about. >>

what file is that, and in what directory?