When I started using Git around 2006, we didn't have GitHub. We used Google Code for SVN hosting, but we wanted to try Git because it was 'truely' decentralized, so we just pulled from other developers' computers directly. It involved setting up port forwarding on the router and letting your computer on 24/7. Fun times.
You can also have an upstream git repo on a local filesystem and add that as a remote.
But when most people talk about a git server that includes collaboration and giving people SSH access just so that they can read from your repo is not reasonable.
This is indeed a Git server. It is not a Git Forge though. Pull Requests, Issues, CI/CD, access management, etc. are about as important as a putting my code somewhere.
I find it strange the websites some of these HN articles are hosted on... going through the effort to write a post before getting a domain outside of .vercel.app is interesting.