Safely finding and deleting system data files on iMac running Ventura

Timbo, I share your frustration - nowhere online, in Apple discussions or anywhere else, does anyone address how to fix System Data - they repeat a long list of ways to delete large files which are readily visible. After starting a chat with Apple on line about this earlier today, I was rapidly connected to a senior tech support guy at Apple, who called me promptly, spent an hour and a half viewing my screen and guiding me through a lot of complicated steps (that I don't fully understand) with the result that my System Data has shrunk from 400 to 41 GB - so I am delighted. I told him that there are lots of posting about this System Data issue, and he said there is no one solution so anyone with that problem should definitely get in touch with Apple for help. By the way I do not have Apple Care and my 2021 MacBook Pro is long out of warranty.

The system itself is only 10.33 GB. The System Data, once referred to as Other, is 125 GB on my 2017 27' iMac:

It consists of a potpourri of files which can include:

• System temporary files

• macOS system folders

• Archives and disk images (.zip, .iso, etc. - often found in the Downloads folder)

• Personal user data

• Files from the user’s library (Application Support, iCloud files, screensavers, etc.)

• Cache files: browser, Mail

• Mail messages & attachments

• Fonts, plugins, extensions

• Safari reading list

• iTunes backups

• Crud resulting from jailbreaking your iDevice

• Game data

• Saved data files

• Call history

• Notes

• Media

• Voice memos

• Other files that are not recognized by a Spotlight search

• Media files that cannot be classified by Spotlight as a media file because they are located inside of a package

• Files created and modified by other user accounts on your Mac.

They can be located anywhere on your hard drive.

The files that you have control over are located in the Documents, Downloads, Pictures, Music and Movies folders.  You can use this free app, GrandPerspective, to find the largest files on your drive so you can determine if they can be deleted or moved to an external HD for storage.

Note: you can empty the Downloads folder after the apps and/or updates that were downloaded have been installed or applied.  Some users have found a couple of Gigabytes of files in their Downloads folder which are no longer needed. 

Thank you Anthony, I found also an experienced Supporter from Apple, who did the same. We looked deep in the System for big folders, mostly cachefoldes which I should delete! From 105gb fix system data I'm now at 27gb and I'm very happy. I had luck, because the first supporter from apple wanted me to erase the whole system and rebuild the Mac. Before she started to assist me, the telephone was interrupted and she didn't called me back. Wenn I ask with the case number she send me for more support, I got the experienced guy, who helped me, like I wrote above.

Freeing up space: 

Free up storage space on your Mac - Apple Support. 

Optimizing Space:

Optimize storage space on your Mac - Apple Support also offers some suggestions.

None of these articles explain what to do about System Data at all