the network appliance is now discontinued and self-hosting the network appliance can no longer happen software-only, you have to use their “server os”, which can’t be run in a container.

Of course it can, they just don’t provide a containerized version but other people do. I use the linuxserver version, it’s regularly updated and works without issue. It uses about 1.2 GB of RAM, so a little heavy, but nothing crazy.