It's been a year since the last season of Stranger Things and production of season four has obviously been held up by the pandemic. According to the show's creators Ross and Matt Duffer, season four, when it finally does happen, won't be the forever finale. From the Hollywood Reporter:
What's the status of shooting season four?
ROSS Everyone's excited to get back to work, but the priority is the safety of the cast and crew, and that will dictate when we go back.
MATT We've had a lot more time to work on the scripts. For the first time, we have all the scripts written and we're able to look at it as a whole piece and make adjustments.[…]
ROSS Season four won't be the end. We know what the end is, and we know when it is. [The pandemic] has given us time to look ahead, figure out what is best for the show. Starting to fill that out gave us a better idea of how long we need to tell that story.