ProtonVPN + Debian Buster/Bullseye

Mate/Gnome:

sudo apt-get install openvpn resolvconf network-manager-openvpn-gnome

KDE:

sudo apt-get install openvpn resolvconf network-manager-openvpn

After that, create new network with «import vpn» option in network manager and import config file provided by ProtonVPN.