For a long time Chrome has been the lone holdout in MathML support, making MathML basically unusable, but there is now support in Chrome 109, which is the current stable version:

https://caniuse.com/mathml

In a short time it should be even more widely deployed.

docutils already has support for generating mathml output, but I don't think Sphinx yet provides an easy way to take advantage of it. I think we may also need some CSS from docutils for it to work well.

MathML's advantage over MathJax is that we don't need an extra javascript dependency, and it would render instantly with the rest of the content. In contrast, with MathJax there is a lag during which you see the unrendered math markup and then the page reflows after it is rendered.