First, you have to remove snapd from the system by

sudo apt-get autopurge snapd

and then create special configuration file for APT, as LinuxMint did:

cat <<EOF | sudo tee /etc/apt/preferences.d/nosnap.pref
# To prevent repository packages from triggering the installation of Snap,
# this file forbids snapd from being installed by APT.
# For more information:

Package: snapd
Pin: release a=*
Pin-Priority: -10

This will prevent Snaps installation in future.