Not very many, and they get caught quickly. The ones that don’t get caught quickly are so subtle that they’re barely useful. Several Valorant cheat developers have completely given up and shifted focus to other games. Plus, Riot makes an effort to “soul ban” cheaters so that they can’t just get a new account and keep cheating. If Blizzard even did this ONE thing, it would go a long way to solving a lot of this game’s problems.
Overwatch has had a kernel-level cheat problem for a long time. It needs to be a lot harder to get away with cheating for more than a few matches. The “ban wave” philosophy is no longer valid in 2020, and cheaters brag about just hopping on another account when they do get banned. Blizzard is asleep at the wheel here. No new game can be successful in 2021 without aggressive anti-cheat.