Mathcha is a great online math notebook. The browser version is completely free, with no ads or purchases. (However, there is a paid download version. The only difference is that it is offline.) The interface is also simple yet robust. Math symbols, drawings, charts and more! Finally, there are also convenient shortcuts for entering certain symbols.
They banned me for "intentionally typing images incorrectly". I was doing the google recaptcha with their official software. Google makes you do them over if it is incorrect, and lets you through if you do a good job. I got them all correct, but got banned randomly. How can I type images incorrectly if they are all clicking, and checked by Google AI? I got them all right too.