Did you know that there is a nice way to type math notation? Like $$ f(x) = 3x^2 + \ln(x) - \sin\left(\sqrt{x-8}\right) \in \mathscr{F}_\mathbf{R}\big([8,\infty)\big) $$ This is based on the document typesetting system LaTeX. To say it simply, LaTeX is a markup language, kinda like a programming language, that makes it super easy to type mathematics. It is the standard tool professional mathematicians and other scientists use to draft papers and notes. Then Overleaf is a website that allows teams to collaborate on documents written with LaTeX, kinda like how Google Docs works with typical documents. Getting started, I’d advise you to use Overleaf. I've written a small annotated LaTeX file in Overleaf that you can copy to get started: after logging into Overleaf you can click Copy Project under the Menu in the top-left of the page. To provide guidance on learning the LaTeX language: the Overleaf website has some nice LaTeX documentation to introduce you to the language. The LaTeX Wikibook is more robust, and the resource I still often reference. Then the website Detexify is invaluable, since it allows you to hand-draw a mathematical symbol to find out the LaTeX command to create that symbol. After you get used to the mechanics of LaTeX, you'll need to develop some style and a workflow. Diomidis Spinellis’s LaTeX Advice provides a good start for this.
A related bit of software that might interest you is TeX for Gmail. This is a chrome browser extension that allows you to type mathematics in an email using LaTeX’s syntax.