Welcome to Derry will explore parts of Derry and It’s past years before the events of the 2017 movie, and the show’s plans for the future show how it can solve a huge mystery about Pennywise’s origin. The world of Stephen King’s It is a lot more extensive than it seems, and after Andy Muschietti’s film duology, his version of the novel will continue to expand. Instead of a third movie, It is expanding with a prequel TV series, set 27 years before the Losers Club came across the shapeshifting creature.

https://screenrant.com/welcome-to-derry-future-seasons-pennywise-origin-op-ed/