Pretty sure that all the way back just after Matrix 3 was released there was a statement from Keanu Reeves in media that he turned down offerings on participating in a fourth Matrix movie. Like forever and he will not talk about it any more. Of course I can't find a resource on that right now because (thanks to nowadays SEO optimizations I guess) the first dozen pages are cluttered with related links on that there will be a fourth movie with Keanu now. Maybe someone else can confirm or debunk this "myth" ...