This will prevent a local storage taking space. The next thing to do would be to turn off iCloud and let all those files exist only in the cloud. If you don't have these, I would suggest making sure you have a good backup and restart to recovery mode and run a disk check to be sure the accounting / filesystem are in good shape. How to delete all local TimeMachine snapshots.

How do I know if a time machine backup is running?.There are command line options to force a purge of APFS snapshots: tmutil thinlocalsnapshots / $(echo '10 * 1000000000' | bc) 2

Second - check for local snapshots tmutil listlocalsnapshots / On more recent OS (2021 and later), open Disk Utility and select view APFS snapshots (command - shift - S) to see the space used by snapshots. Your 40 GB of space that could have been 40 GB of documents will show up as grey colored System once the process completes. One easy way to check space is to open the system information app (or look in storage portion of about this Mac) and give it several minutes to catalog all the space into buckets. Here are some details on snapshots from 2019. If you run low on disk space, they take no space locally and exist in the cloud only, downloading on demand. You should also not be deleting the stub files in iCloud.

Just like a backup where the point is to go get a copy of a file you deleted after the delete, snapshots show the contents of a disk in the past and allow you to grab a copy of a past file while that snapshot exists. On the assumption that you have APFS file system, macOS 10.14 Mojave, and local snapshots - the system might take some time to purge the space.

Clear up space on mac