As per https://www.htpcguides.com/force-torrent-traffic-vpn-split-tunnel-debian-8-ubuntu-16-04/, but with few upgrades.
Everything in one script: https://github.com/GAS85/pia/blob/master/split_tunnel_VPN.sh
- Ubuntu 16.04
- Ubuntu 18.04
- Ubuntu 20.04 - DNS issue, different mechanism, read comments.
- Ubuntu 22.04 - DNS issue, different mechanism, read comments.