Here's a simple formula editor using SVG for quick note taking in GNU Emacs. I've added few more commonly used notations.

Code:

https://gitlab.com/atamariya/emacs/-/blob/dev/lisp/svg.el

Video: https://youtu.be/1343m3LY4mo

Details: https://lifeofpenguin.blogspot.com/2021/11/formula-editor-in-gnu-emacs.html