Do you mean the individual .git repository tracking changes in a given directory? Or the remote repository server that you push your changes to and can pull other's changes from? The first one is the fundamental requirement of using git at all, the second is where it gets less trivial.

It's not that the software isn't available. Off the top of my mind, Gitlab offers their community version for free to download and host yourself. I think they even have a Docker image. All you need is to figure out how you would like to do that.

It's the usual question of self-hosting - where would you host it? A server at home? The cloud? Should others be able to access it? How? What about security?

Remotes already hosted by others are just a lot more convenient. You don't worry about the infrastructure, you just push your code. People like me might get more excited about setting up than the actual coding. It's the bane of half my projects - gotta get that git workflow in place, think long-term, set up the "mandatory PR with tests before merge" and shit until eventually I have everything set up... and the spark of the original script I wanted to do is gone.

If you want to focus on coding, the benefit of having a ready setup are hard to dismiss.
On the other hand, setting up and configuring a server can be a one-time job, so if that's worth it to you, power to you!