Newton had given up on trying to grind non-spherical surfaces. He’d tried it in 1666, but the technology of the time wasn’t up to the challenge. A sphere is the easiest shape to grind. Non-spherical shapes are very difficult to grind. In fact, astronomers would have to wait until 1721 for John Hadley to grind the first non-spherical telescope mirror.
Newton made two reflecting telescopes, but neither was used much. Their purpose was more to prove Newton’s ideas about telescopes than to view the sky. Although other scientists would have to improve Newton’s design before these types of telescopes became popular, today we still call them Newtonian reflectors, after their creator.