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 pre-containerized version but other people do. The server software just a regular program that you can install on any Linux OS. I use the linuxserver Docker version, it's regularly updated and works without issue. It uses about 1.2 GB of RAM, so a little heavy, but nothing crazy.
https://docs.linuxserver.io/images/docker-unifi-network-application/