I recently signed up with ProtonVPN.
Here’s how I connect in Arch Linux.
sudo pacman -S openvpn
sudo wget -O protonvpn-cli.sh https://raw.githubusercontent.com/ProtonVPN/protonvpn-cli/master/protonvpn-cli.sh
sudo chmod +x protonvpn-cli.sh
sudo ./protonvpn-cli.sh --install
sudo protonvpn-cli -init
sudo protonvpn-cli -connect
sudo protonvpn-cli -disconnect