Joke about is a noun eg He told a funny joke about a dog Joke around or to joke around is a verb and refers to having fun, maybe telling jokes or playing pranks. You'll hear it as an excuse if someone gets offended or there's an accident eg I was just joking around, I didn't mean for that to happen

"joke about" = "a funny story on the subject of" "joke around" = "play"

没区别，只是英美偏好不同 About and Around: The difference between about and around is more straightforward and largely a matter of preference: about is more common in British English and around in American English (Pocket Fowler's Modern English Usage, p. 8). https://www.editage.com/insights/scientific-writing-difference-in-meaning-of-about-around-and-approximately

Joking about something is more about something specific. Joking around means being in a silly mood and making jokes about more than one specific thing.