If you are upgrading from Ubuntu 20 to Ubuntu 22 using ‘do-release-upgrade’ and get a fatal error ‘Connection to the the Snap Store failed’, this may be resolved by removing the ‘lxd’ package which is a lightweight container supervisor.
sudo /etc/init.d/lxd stop sudo rm -fr /var/lib/lxd sudo dpkg --force depends -P lxd; sudo dpkg --force depends -P lxd-client sudo apt upgrade -f -y
After making this change, run ‘do-release-upgrade ‘again.
REFERENCES
askubuntu.com, Your system is unable to reach the snap store
ubuntu.forumming.com, Your system is unable to reach the snap store