Comment by devilbunny

Yeah, if you 1) trust that they actually know how to write a screenplay (a very different skill from writing a novel) and 2) believe they won't sue you for stealing their idea.

That's a problem with fanfic in general. People who would have written fanfic ten or fifteen years ago are writing stuff like litrpg's now; you can steal the general concept as long as you don't rip off the details. And it's a big enough world that you can practice your writing and actually become decent at it before you try to take on a big work. If you compare early drafts of, say, Dungeon Crawler Carl to the latest books in the series? You can see the skill improvement.