It's been a thing for a long, long time, and I've always felt kind of weird about it.
I mean, I am totally okay with fanart/fanfiction/whatever about just about any fictional character imaginable, whether they are played by an actor or whether they're animated, drawn in a comic, or just a character from a novel. They're fictional - do whatever you want with them.
But once the fan-creators start blurring the lines between character and actor, or when they straight up create stuff about real people (fanfic about real people commonly being referred to as RPF - Real Person Fiction) that aren't playing any kind of character, that starts getting into murky territory for me. Just drawing portraits - fine. A portrait is just a picture of what a person look like. But fictional speculation about real people? Eeeeh. I don't know. Everyone's free to do whatever they want, but RPF has always felt a little... disrespectful, I guess is the word?
These people might be public figures, but they still have some sort of right to the narrative of their own lives. I mean, you wouldn't be okay with it if tabloids printed outright lies about someone, claiming they had a sexual orientation they didn't have, right? You'd think the tabloid was out of line. So why should we hold ourselves to a lower standard?
Yes, it's just for fun, and yes, it's impossible to control the weird world that is internet-fandoms, but still. RPF makes me kind of uncomfortable.