Hey all,
I've been battling my mac's storage space for the past few years, where- sometimes- it would randomly fill up all of my remaining storage, seemingly with nothing? This got logged as System Data in the breakdown, which isn't totally helpful. When restarting the computer, this phantom data would all vanish- but sometimes, fill back up in as short as 20 minutes.
I never could get a good answer from customer support (I don't think they knew either), so after finally breaking down and doing some self research, I tracked the cause for me- that being, that Mac auto-downloads the default background wallpapers, in 4k, 240fps, even if you don't use them as your background. They're very nice videos, but it'll sometimes download them en-masse, causing 5-25 gb to mysteriously vanish with no clear reason.
To check if this happened to you-
1: Open finder
2: At the top of the screen, click Go -> Computer (note: you do need just 'computer'; the library we navigate to later is different than what Go's "library" option will bring you to. Confusing, I know)
3: Go to your hard drive, and then into Library -> Application Support -> com.apple.idleassetsd -> Customer -> 4KSDR240FPS (note: You made need to enable hidden folders to see the library folder? I don't quite remember, but if you don't see it, check another guide on how to reveal hidden folders)
4: Check the videos in there to see how much space they are taking up.
~~~
Now then- if that is eating up all of your storage, how do you fix it?
Please note, I am not a tech-spert at all. Fuck around with system files at your own risk. I'm simply relaying my own experience for you to use as a jumping-off point, not to copy verbatim without thought. Okay? Okay.
To fix it, I:
1: Changed my background & screen saver to custom ones, to avoid needing the Mac defaults
2: Went into the folder listed above, and deleted all the videos
3: Cleared out my trash to permanently delete them
4: Dragged the folder to the "favorites" section of finder, so I could quickly access it later if need be
Note that this isn't actually a permanent solution. The backgrounds'll probably decide to download again, seemingly at random- you might get a few minutes of peace, or maybe a few months of peace. No real way to know.
But, it's at least more convenient than restarting your whole computer every 20 minutes for weeks on end, so I thought I'd share my findings~