Monterey: disk space is not freed even after deleting very big files

There are times that Spotlight's index doesn't get updated immediately upon a file deletion.

So try the following in order as needed:

1 - How to rebuild the Spotlight index on your Mac - Apple Support  

2 - boot into Safe Mode according to How to use safe mode on your Mac and test to see if the problem persists. Reboot normally and test again.

NOTE: Safe Mode boot can take up to 3 - 5 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

Not to be insulting, but did you remember to empty the Trash?

Also, deleted items may remain in any APFS snapshots until those snapshots are deleted. Usually these snapshots are made by Time Machine or other backup apps. Once those backups have been transferred to external media, those APFS snapshots will be automatically deleted. See these articles for a bit more information:

View APFS snapshots in Disk Utility on Mac - Apple Support

https://derflounder.wordpress.com/2018/04/07/reclaiming-drive-space-by-thinning-apple-file-system-snapshot-backups/

Edit: Also, did you make copies of any of these large files on the same internal volume? If so, then due to how the APFS file system works you just deleted a link to the actual data. You must delete every link to that data for the data to be actually deleted.

https://bombich.com/kb/ccc5/everything-you-need-know-about-carbon-copy-cloner-and-apfs#cloning

https://eclecticlight.co/2020/04/14/copy-move-and-clone-files-in-apfs-a-primer/

Notation - If the user is using a cloning software like Carbon Copy Cloner - suggest tweaking the Safety Net Feature in this software. It may be making addition Snap Shots that are not being Cloned to the Eternal Drive. If this should be the case, these Snap Shot could be using additional space on the drive 

dagmar83 wrote:

What is happening here? (this started on Monterey, other systems behaved liked expected)

I think you must not have noticed the problem before, or you had more free disk space before. This has been normal behaviour for a few years.

You aren’t actually allowed to delete files anymore. All you really do is flag them for deletion. They will be saved in a local snapshot until local snapshots are purged. This should happen within 1-2 days. I recommend keeping 100 GB of free space to avoid problems. Note that I said “free” space. Your “available” storage doesn’t mean squat.

Did you check for snapshots using either of the two methods I linked? It is possible CCC is only showing CCC snapshots and is ignoring any macOS created APFS snapshots.