> It consisted of running tmutil from the command line and giving it a bunch of command line arguments that did not seem to make sense or have any correlation to the thing that I wanted to do.
It’s not completely obvious, but when you delete something it doesn’t disappear immediately because your Mac will keep it around on a local Time Machine snapshot so that it can keep decent history even if you’re away from your backup drive for a bit. And even if this wasn’t the case, with APFS copy-on-write deleting a file won’t necessarily free up space on your filesystem if there’s another copy hanging around.
It’s not completely obvious, but when you delete something it doesn’t disappear immediately because your Mac will keep it around on a local Time Machine snapshot so that it can keep decent history even if you’re away from your backup drive for a bit. And even if this wasn’t the case, with APFS copy-on-write deleting a file won’t necessarily free up space on your filesystem if there’s another copy hanging around.