For math symbols I use Unicode characters, I have XCompose shortcuts [0] to easily insert them. I'm currently using WinCompose to use the same shortcuts on Windows. This works fairly well for my use cases (programming language theory and undergrad math), but doesn't support the fancy layouts that LaTeX does (fractions, large sub/superscripts).

I don't have a good solution for graphs/pictures/drawings. I don't think I've ever needed to, if I did I think I would just put the image in a folder alongside the note (`YYYY-MM-DD-ext`).

[0] https://github.com/CoderPuppy/.files/blob/master/XCompose