I have a 2020 MacBook Air with – theoretically – a 1TB solid-state drive.
The Finder says I have only 64.4G free; Storage in System Settings says 935.2G is used, 411.6 of which is "System Data". CleanMyMac similarly says 941.64G is used... BUT when I run its Space Lens, it finds 575.3G under Users, 74G under Applications, 12G under Library, 11G under System, and less than 10G for everything else. That should be no more than 700G used - and it doesn't mention any "System Data". (GrandPerspective gives me a similar result.)
What is this "System Data" that's eating the remaining 200+ gigabytes of my hard drive, and how do I get rid of it? This thread suggested that updating your OS or turning on Full Disk Access in CleanMyMac could help solve it, but I did both and neither worked. CleanMyMac also didn't find any malware, even on a deep scan. I've heard it suggested that Time Machine backups can be the culprit for this sort of thing, but I have Time Machine set to back up to an external drive, as far as I can tell.
Performance has also been really slow in general lately (it'll often take several seconds to open a folder in the Finder when I click on it). I had a brand-new SSD put in in late 2021 (after a coffee spill); it doesn't seem likely that a drive would be giving up the ghost after less than two years. Something's clearly gone wrong here but I really can't tell what.
