I was using Apple Notes for some “math thinking” the other week. A killer feature for me would be an easy way to input various math Unicode characters (I was just copy and pasting them).

There are various stylus-based tools which do that sort of thing:

https://www.inftyproject.org/en/software.html

(I used to use the math input palette w/ a Wacom ArtZ on my NeXT Cube for transcribing math documents in college)