Would you ever write self-insert?

I mean, isn't all fiction ultimately self-insert?

But if you mean would I write a story where a middle-aged nerdy Danish librarian starts hanging out with our more ferocious iron age ancestors or random superheroes & villains or ancient fantasy!Chinese sorcerers? Probably not. I don't even do much in the way of OCs.

Of course, this is writing we're talking about. Let's not talk about the stuff that doesn't ever make it out of my brain and onto paper.