How did the myth of Jesus' resurrection originate?

[Mudhammam]

Again, the claim that "paul" is first century is part of the story. We have no first century manuscripts of any "paul." We also have no Greco-Roman sources which mention xtians in the first century in any of the places that "paul" claims to have established churches.

In 1936 Margaret Mitchell wrote Gone With The Wind about actual events in American history and created a whole cast of characters to populate her book. That does not make any of her characters "real."

I don't know any scholars who would take your Fictional Paul hypothesis seriously. There's no reason to think the Greco-Roman world would take notice of such a marginal group in the first century (unless of course the Resurrection actually occured).