I've now followed the "how to clean Linux Mint safely" guide I saw recommended (at least the relevant parts), as well as tried other suggestions, yet my root filesystem is still full. There's just one old kernel, Timeshift has no backups, thumbnails, logs, fonts, and software packages are all gone. I think. The exception is a few gigs of flatpaks which won't delete but I don't think that's the real issue. The only advice I haven't followed was essentially "open disk usage analyzer and delete th…