What i found to work the best is to generate and download a config file, then import it into NetworkManager. There’s a plugin for wireguard here: github.com/max-moser/network-manager-wireguard
This way, it’s easy to add routes, autostart, etc. But I don’t think a safe killswitch is possible.
Edit: But since this is a piracy community, i should mention that qbittorrent has a setting for specifying the network interface, so it’s easy to force it to use the vpn connection only, in place of a killswitch.