I’m uncomfortable not only with real-person fanfic but fanfic involving characters played by real people. So I stick with cartoon fandoms. And mostly Western ones, because I’m not a big enough anime fan to have seen a lot of the ones people tend to write about.
The only non-cartoon fanfic I’ve ever written was about Adam and Eve, because that’s not a particularly recent fandom.
I’ve gotten unsolicited requests that try to push me into writing for fandoms that I know nothing about. Guess that’s my hard stop for writing, along with the desire to finish what I’ve already started. And TBH, if I had fallen into the potter universe today, it’s unlikely that I’d even delve into fanfiction.