I will be releasing a separate Joomla 4 version for each of my extensions and I'm aiming to have some ready in the next few weeks but this will also depend on any bugs that arise in the Joomla core code as more users staring using it.
If you want to contributed to a project hosted on GitHub you will find the majority of the projects ask that you do it in the form of a Pull Request. If you want to learn more about how to submit a pull request try this guide.
Do you want to change the user that is automatically selected when committing with git? I having been using Git and Netbeans/PhpStorm for a long time but I had a niggling issue that I finally got around to solving, how to control the default Author and Commiter.