Just be aware that using a vpn this way requires you to configure a firewall if you want an effective “kill switch”.
I block all traffic by default, then allow all traffic through vpn virtual adapter (ie tun0), and only open the necessary network ports to allow vpn connection establishment (ie 1195 udp for expressvpn ovpn sha512).
This way if the vpn connection drops unexpectedly there is no network connectivity.
Otherwise if a network manager ovpn connection drops all traffic will revert to the default network connection, exposing your real (ie ISP) IP address.