This is not a question, but a small tip on how to do it. You can use LaTeXiT to create complex formulas or even beautiful tables. It allows you to include any LaTeX package by adding them to its preamble in the settings.
Unfortunately, you need to copy and paste the generated PDF manually via right-click, which makes it difficult to access the original file for the formula or table later.
For the uninitiated, LaTeXiT requires the installation of an updated TeX (e.g. MacTeX) distribution so it can find the referenced packages in its preamble section. This is fine for those of us familiar with [La]TeX, but for the uninitiated, the learning climb will be steep.
Beginning with Keynote 8.1, Apple introduced an equation editor using the blahtex translator to convert LaTeX to MathML, or just MathML as an equation object in the Keynote slide. When double-clicking the embedded equation, one opens the equation editor to reveal the input source.
About LaTeX and MathML support in Pages, Numbers, and Keynote - Apple Support
MathType no longer works with Keynote 8.2 on Mojave or later for those thinking of that as an alternative Math input solution.
Mathype is not working with Keynote afer … - Apple Community
problem in adding quantum equations or complex table in keynote
