I use MathJax a lot cause I use Anki.
For whatever reason, it is unclear to me what exact subset of LateX syntax has been implemented on MathJax. Also, very frustrating is that _how do I do X_ type questions with LaTeX on Stackoverflow have responses which involve installing custom Math packages and such. Again, no idea how to do that with MathJax in an easy way.
All this considered, I am not sure why I'd use Math on Github. Like if I was collaborating on a paper, surely overleaf is a less painful solution. I do use version control with tex files, but I don't depend on github to render the tex files.