These patches are based off Mastodon v2.7.1. They will probably need some work to apply to future releases.
mathjax.diff adds MathJax to render LaTeX. You need a copy of MathJax under the URL
Write inline maths between
\), and display-mode maths between
autolatex.diff adds automatic replacement of some LaTeX with unicode equivalents in the toot compose box. It only applies to text not within LaTeX delimiters, so doesn't interfere with MathJax.