All you need is a 64bit Linux that can run a somewhat recent version of Docker as well as run bash scripts (e.g. launcher).
It doesn’t have to be Ubuntu. Fedora, CentOS, Arch,… all of them should work. Using a supported LTS release of Ubuntu is just a recommendation. And that’s essentially what’s been written in the documentation.
The default of the current supported LTS release of Ubuntu Server works fine. At minimum, a 64-bit Linux OS with a modern kernel version is required.
You can chose whatever x64 OS / version you are comfortable with as long as it has a recent Docker version. The launcher script might not be able to automagically setup everything if it’s not a Debian/Ubuntu based distro, but other than that it should work nearly everywhere.
I’m closing this topic as the discussion isn’t going anywhere.