First, look if You have installed Snap Programs. that you can do with the Terminal. Open it and type snap list
When Snap Programs are installed and you want remove them type snap remove --purge [Package-Name]
After that You should turn off Snap. To do this type in the Terminal:
sudo systemctl stop snapd
after that:
sudo systemctl disable snapd
Then comes the Uninstallation. For that type in the Terminal:
sudo apt purge snapd gnome-software-plugin-snap
After that type sudo apt autoremove to delete the Rests from the Uninstallation.