The Back to the Future franchise was a smash hit, but the story never progressed beyond Back to the Future Part III. Of course, many would have been thrilled if Back to the Future 4 had become a reality. These movies are cult classics, and the fact that Marty McFly’s story revolves around time travel makes a sequel possible in just about any decade. According to Back to the Future creators Rober Zemeckis and Bob Gale, Universal has continued to poke and prod them for another movie to continue the story. However, Back to the Future 4 has yet to happen.

https://screenrant.com/back-to-the-future-4-why-never-happened-explainer/