trillian

I am not sure if this is helpful but I just created a systemd unit that sets up the network namespace in the background. Then, as I use nixos, I add the wireguard VPN to nix and with networking.wireguard.interface.name.interfaceNamespace you can then move it into the container. For running applications I cannot really comment because I have only one service making use of the VPN which runs inside a NixOS container for which the namespace can be configured with --network-namespace-path=/run/netns/…

Did you look into network namespaces? With these you should be able to dedicate a namespace for the VPN adapter and then move discord into it, at least with wireguard it works flawlessly.