System Data Files Have Taken Over My New Mac mini

Long-time Mac user and owner of dozens over the years and I never ran into this.

New Mac Mini System Data files have grown to 80% of my system choking out any more space. Been reading around and issue and solutions seem nebulous and aren't working.

I have...

• Empty the Trash in the Dock.

• Empty the trash in the Photos app.

• Delete unused and unneeded installers from your downloads folder and desktop.

• Reboot your Mac at least weekly.

• Transfer files that you don’t use daily to an external drive. Files that take up the most room are movies, images and music.

Barely made any impact as I didn't have much material there. Also, looked at cache folders in the library I've been advised to leave but empty contents but find there is very little there. Time Machine is not set up either.

All the advice I see warns to be 'careful' but I'm not particularly a techie so I'm feeling a bit stressed about how to proceed especially, again, since I haven't run into this problem before.

I use an External HD for most of my data including music and photos.

Please advise! Thanks you.