Deleting Time Machine local snapshots

The Apple article I linked allows you to view & delete APFS snapshots if they exist. Just make sure you first click the "Data" volume so that the "Show APFS Snapshots" option appears on the Disk Utility "View" menu on the menu bar.

I don't use DropBox, but are you sure those files were fully removed from your local drive? It is possible it may take some time for that process to complete depending how the DropBox software works. You may just need to give it a bit more time to complete its process.

Purgeable space is controlled by macOS itself and can even include data from file syncing services such as iCloud. Maybe try booting into Safe Mode for a moment, then reboot normally to see if that may trigger anything to clear up.

Unfortunately there is no good way of knowing what data is taking up this Purgeable space. There are some places even within your own home user folder where you cannot see what is on the drive even when elevated to a root user on the command line due to the new privacy & security features Apple has implemented into macOS. Even APFS snapshots are hidden from view except when using the instructions I linked or when using the special command line utility to view them.

1. Check Time Machine Settings:

- Open System Preferences from the Apple menu.

- Click on Time Machine.

- Ensure that automatic backups are turned off by unchecking the box next to "Back Up Automatically." This should prevent Time Machine from creating new local snapshots.

2. Delete Local Snapshots via Terminal:

- Open Terminal from the Applications folder or by searching for it using Spotlight.

- In Terminal, enter the following command to list all local snapshots: tmutil listlocalsnapshots /

- Identify the snapshots you want to delete based on the timestamp.

- To delete a specific snapshot, use the following command (replace [snapshot_name] with the name of the snapshot): sudo tmutil deletelocalsnapshots [snapshot_name]

- Enter your administrator password when prompted.

- Repeat this process for each snapshot you want to delete.

3. Restart Your Mac:

- After deleting the snapshots, restart your iMac to ensure that the changes take effect.

4. Check Disk Space:

- Use Disk Utility or Finder to verify that the local snapshots have been successfully deleted and that disk space has been reclaimed.

5. Monitor Disk Usage:

- Keep an eye on your disk space usage over time to ensure that it remains within acceptable limits. You may also consider regularly backing up important files and data to an external drive to free up additional space on your internal drive.

If you continue to encounter issues or if the local snapshots persist despite your attempts to delete them, consider contacting Apple Support for further assistance. They may be able to provide additional troubleshooting steps or guidance specific to your situation.

Here is a link to an Apple article with instructions for viewing & deleting APFS snapshots:

View APFS snapshots in Disk Utility on Mac - Apple Support

Here is another post I wrote regarding macOS storage terminology which may help you better understand things.

macOS Storage Terminology -- hwtech - Apple Community

It is very unfortunate that Apple decided to focus & use "Available" instead of "Free" storage space since the latter is the most important value. You need to always keep at least 20GB+ of Free space at all times for the normal operation of macOS. For some people they may need to keep 100GB+ Free if there workloads involve large projects such as video editing.

I ran across an interesting YouTube video that describes a strategy to free up the System Data on a Mac running Sonoma. Here's the link: Free Up System Data on Mac

I mention this because it appears, from what I saw in this video, that Adobe products leave a lot of "stuff" that gets thrown into the System Data...and a lot of this "stuff" can be cleared out. You mentioned Photoshop, which is why I thought of this video.

Hopefully it helps.

Interesting, someone else is noting a scratch disk issue, I wonder if it is Photoshop related:

24", M1 iMac keeps running out of scratch… - Apple Community