I can’t provide full support for that plugin as I have nothing to do with the project. When you download the zip file from Github, open it and find the addons directory. Zip the folder inside addons and use that in Blender. The other files are all the code used to compile the plugin.
Depending on which branch you downloaded, this addon/plugin may be named the same as the default Blender GLTF importer/exporter. That creates a conflict. There are some branches in that repo that have renamed the plugin. In the Blender import tab, there will be a different listing for the MSFS gltf format.
This entire process is a little tricky and not well documented. But when it works, it’s quite a nice development effort.