I've been using LaTeX for about 5 years now. I don't recommend picking up TeX notation for reading maths in plaintext. It's the nicest way to produce nice looking mathematics PDFs or MathJax, if you have a powerful text editor. And after a while, you learn things like "underscore is for subscript" and "^ is for superscript".

But the point is, mathematics written as a plaintext document needs an interpreter, unless you have been writing papers with math notation for some years. But it is still far more cumbersome (and looks ugly) than writing formulas by hand. And that's not exactly plaintext learning material anymore, then, even though the sources are text files (unlike Word documents).

My ideal workflow (the one I dream about) would be a document camera -like setup that parses math I write on a paper (or a blackboard) into LaTeX (or MathML) style format and ~immediately renders it as beautiful document (with MathJax or similar tool). Like Overleaf, but without typing. (And of course then I could open the source file in text editor to make edits.)