Don't forget to purge those, as well:
sudo apt purge snapd flatpak
sudo apt clean && sudo apt autoremove && sudo apt autopurge
sudo apt-mark hold flatpak <- Prevents flatpak sneaking back onto the system via dependencies
sudo apt-mark hold snapd <- Prevents snapd sneaking back onto the system via dependencies (such as when installing Chrome)
sudo umount /snap
sudo rm -rf /snap
sudo umount /var/snap
sudo rm -rf /var/snap
sudo umount /var/lib/snapd
sudo rm -rf /var/lib/snapd
sudo rm -rf /etc/apparmor.d/usr.lib.snapd.snap-confine.real
In sudo nautilus, search for 'flatpak' and delete all files that match that search.
If you're running the ZFS file system, DO NOT do a search for 'snap' or 'snapd' and delete all files that match that search... the ZFS file system has some files with that in the name... lesson learned the hard way.