My guess will be hibernation file and swap. If any of those had suspend to disk enabled, the hibernation file will be the same size as installed Ram… which can take up a good percentage of that used space. I have a pretty bloated xUbuntu install on my system right now and it’s sitting at 10.6GB. Including swap and /home, but no hibernation file.
Then don’t remove snaps and you don’t have to mess with anything out of the box.