How can I safely clean up storage on my Mac mini Tahoe 26.3?

Apps of that type are particularly dangerous to your own personal files. How can a piece of software know better than you what to keep? To say nothing of the problems that will pop up when it deletes files important to the proper operation of any other software.

Space management is a lot to do with personal file management, says my ocd self.

What you can do to tidy up your storage/space:

• Make judicious use of folders and folder nesting throughout the Finder.

• For the Desktop, take advantage of Stacks and file grouping.

Use desktop stacks on Mac - Apple Support

• Reboot your Mac at least weekly. Let the OS do housekeeping and clear caches.

• Empty the Trash in the Dock. 

• Empty the trash in the Photos app.

• Delete unused and unneeded application installers from your downloads folder and desktop. No need to store on your Mac what you can freely download any time.

• Transfer files that you don’t use daily to an external drive and then delete them from the startup drive and empty the trash. Files that take up the most room are movies, images and music.

• Don't install junk.

This from Apple on the subject of freeing up space:

Free up storage space on Mac - Apple Support

Also, please see this guidance from Apple: 

Find and delete files on your Mac - Apple Support

You're welcome.

It is still possible to use Apple's storage optimization tool to help manage space on the Mac.

It may be helpful, but imho, the onus will always be on us users to do some manual housekeeping from time to time. There is no app that can know what files are most important to a given user.

Optimize storage space on your Mac - Apple Support

lazart wrote:

I thoroughly clean up photos, music, and movies on a regular basis. I am concerned about the unknown, system data

You could try starting up your Mac in safe mode every now and then.

Start up your Mac in safe mode – Apple Support

One thing this mode does:

• "Clears some system caches, including font caches and the kernel cache, which are automatically created again as needed. This can temporarily make more storage space available on your startup disk."

Presumably macOS knows which caches are safe to remove and which files should be left alone. After starting in safe mode, use  > Restart "to leave safe mode and restart your Mac normally"

lazart wrote:

I read that it is not safe to use software to clean my Mac (like Dr. Buho or CleanMyMac).

There is DaisyDisk .

I haven't used it, but from my understanding, its appeal is that it helps you to see which of your own files take up lots of space. The developer says that "No automated cleaning is performed — this excludes the potential risk of damage to system and application components."

They have a page on purgeable space that is interesting. Apparently, if you have enough free space, the Mac may allow temporary things like Time Machine snapshots, caches, swap files, etc. to "pile up to as much as 80% of the disk's capacity, by design." The idea is that macOS will automatically dump some of this stuff to reclaim the space, if needed, but in the meantime, it's apparently trying to put that disk space to work holding caches – much as it will put free RAM to use holding "Cached Files" (Activity Monitor).

One way is as follows:

1 - get an external 1 TB SSD and format it APFS. OWC (MacSales.com) is the source I recommend. They have several depending on your needs, work flow and budget.

2 - copy your biggest folders, Pictures, Music and Movies to the external SSD. Rename them Pictures-2, Music-2 and Movies-2.

3 - make sure the three libraries work from the SSD before deleting the contents of the three original folders. Do no delete the original folders.

4 - this should remove enough files from the boot drive for you to have plenty of free space. I try to maintain a minimum of 100 GB or more to facilitate optimal system and application performance.

Just some food for thought.