Desmos is decent IME (am an u/g, so I've used it occasionally); I don't think I ever had serious issues with typesetting (backspacing between sub and superscrip

Desmos is decent IME (am an u/g, so I've used it occasionally); I don't think I ever had serious issues with typesetting (backspacing between sub and superscripts is occasionally awkward, iirc), but navigating the site and using advanced features was always troublesome. I had to fallback to Googling for a specific Desmos calculator a lot.