I don’t know of a good way to route other application’s traffic through the VPN container with them being in docker containers, unless you use some intermediary setup. That’s why I have socks proxies routed through the VPN, so I can selectively put traffic through it. If the app supports a socks proxy you could do it that way. At the least you could use Proxychains to do so if the program does TCP networking.
It depends on how many versions I am away from the latest, and how much I’ve messed with the distro.
Usually I stay on an Ubuntu LTS and upgrade from LTS to LTS when that upgrade path is ready. I upgraded from 20.04 to 22.04 this way.
But this time I wanted Pipewire in 24.04, and didn’t want to wait for a 22.04 to 24.04 upgrade to be ready. I’m using a bluetooth headset and Pulseaudio is pretty terrible at switching headset profiles. Between not wanting to upgrade an upgraded install, and having messed with Pulseaudio quite a bit trying to get it working, I went ahead and clean installed 24.04 and moved some configs over.