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.
For me, it’s more on the practical side of where I want to be spending my time, and I prefer spending it on writing my own creations—it’s fun! So, unless I get really motivated, I don’t expect to venture into new fandoms for writing.