MacOS Sequoia System 15.3.1 data M1

Part 1 of 2

System Data: Contains files not listed here. It includes system files like log files, caches, VM files, and runtime resources. Temporary files, fonts, app support files, and plug-ins are also included.

You can’t manage this category’s contents. macOS manages them, and the size varies based on your Mac’s state.

Users have control over the User Account Folder (Home Folder). All other areas are inaccessible.

Purgeable Space is controlled by the operating system. When the system needs more empty space, it moves some purgeable space to empty space.

There’s no user action to hasten this transition. It can take days or longer.

The links below help identify what’s taking up space on the internal drive and provide ways to remove user-controlled data (Home Folder).

Rebuild the Spotlight index on your Mac.

What is “Other” storage on a Mac, and how can I clean it?

Free up storage space on your Mac.

GrandPerspective

How to delete Time Machine snapshots on your Mac.

This often occurs if the Time Machine Drive isn’t attached to the computer and TM Backup is set to run on a schedule.

TM Backup makes snapshots on the internal drive until the Time Machine Drive is attached. Then, the snapshots are transferred to the external drive.

View APFS snapshots in Disk Utility on Mac - Apple Support (CA)

See used and available storage space on your Mac.

Locate backups of your iPhone, iPad, and iPod touch.

Delete a user or group on Mac

If you use a suite of Adobe applications on this computer, they may create large cache files that can be removed. However, the Adobe cache files will be recreated as the applications need them.

https://helpx.adobe.com/ca/premiere-pro/kb/clear-cache.html

The same clearing of System Cache files can be achieved by booting into Safe Mode. They will be recreated as the system requires. 

Part 2 of 2

From another contributor @etresoft regarding Free Space and Available Space 

Free vs available disk space huge differe… - Apple Community

Quote >>  “ The "available" storage is the amount of used storage that the operating system could automatically delete if it felt that it was really necessary. The "free" storage is the amount that you can actually use for something.

There are system processes that run in the background and automatically delete some of the "available" storage and convert it to "free". If you completely run out of storage, then those system processes will try a little harder. When you "delete" files you are just hinting to the operating system that you don't need those files anymore. The operating system will eventually remove them, but on its own schedule.

Certain tools will allow you to force the issue and manually clean up some of this storage and manually delete local snapshots. But that is only temporary. "  << End Quote 

You could get a reasonable idea of what's taking up space by:

Shutdown and then Boot into Safe Mode so only Apple apps are running and most caches get emptied.

Empty Trash and Junk folders.

Turn off Mail, iCloud access, and anything that's connected to remote storage.

Open a Finder window, set it to List View, then select the option to show folder/file sizes.

Then starting at the top (Macintosh HD) level of the directory tree, progressively drill down, opening each folder, and observing the folder sizes.

Focus first on just a few large size folders in each directory to save time.

Eventually you'll get to folders that contain lot's of what looks like superfluous large files.

!!!MAKE SURE YOU'VE BACKED UP BEFORE DELETING ANYTHING!!!

Don't delete anything until you're absolutely sure they're superfluous.

There are hidden files and folders you could unhide and look at, but they're hidden for a reason. Leave them alone!

!!!MAKE SURE YOU'VE BACKED UP BEFORE DELETING ANYTHING!!!

My M3 iMac is using 34.83 GB