So, it seems like .withMathTex combined with MathJax might be a solution? Is it possible to embed the needed .js into the html easily (goal is to be able to share a singe flie)? I’m ignorant in html things.
Edit. It seems I found my own answer. Installing MathJax (8.19.1 for me) where the C# is run and using for example
Chart2D.Chart.Line<...>(...).WithMathTex(true);
Does produce latex, apparently in any text element, and the html files alone seem to be all that is needed to share/render the result as far as I can tell! I guess somehow I originally thought this was only for plotly.js, maybe based on older information.