What are the dangers of running Flash on Mac?

I've heard a lot of articles say how bad Flash is, but what can it actually do? I've played browser games that use Flash in Chrome, and now Firefox. I know I have a real version of Flash, and I haven't ever noticed anything suspicious on my computer. What can Flash do just by being run? (My Flash is up to date, but I've been using it for years, so I've used different versions at different times). Is there anything specific I should look for? (MacBook running latest version of Mojave)