The above error is happening because APT Package Manager blocks the installation of snap packages. With Linux Mint 20, the Mint dev team has disabled the snap or snapd support by default.
Though Linux Mint has never supported the snap, it has allowed installing Ubuntu snap store or snapd open-source client in previous releases by default.
Hence, now if anyone wants to install snap apps, they need to first enable snap support. For that, there is a solution as well.
To enable snap support on Mint 20, we can do either of two things:
nosnap.pref file in the directory
/etc/apt/preferences.d by running the command:
sudo rm /etc/apt/preferences.d/nosnap.pref
Comment the three lines of code in the same file.
Pin: release a=*
sudo apt install snapd
Then, any snap apps:
sudo snap install <app-name>
There is also another method as well to install snap packages without interfering with
nosnap.pref file. That is, installing app using version number:
sudo apt install <app-name> snapd=VERSION