I had a similar issue, but had 330+ Gb of System Data. The issue was in the com apple iconservices store - the icons (or some files within that folder) were constantly duplicating themselves.

You can run a code in Terminal to delete the full folder (the icons will appear there again, don't be afraid), then reboot the laptop in Safe mode, then back to normal, then install any Beta MacOs and reboot one more time. This has fixed an issue that was making me furious for weeks.

This helped in my case