The first episode of "The Lord of the Rings: The Rings of Power" ends with the arrival of a mysterious person known as The Stranger, played by Daniel Weyman.
Stranger Things Season 4 Volume 1 ended with quite a few unanswered questions. Why was time frozen in the Upside Down to November 6, 1983? What really is Will's connection to the Mind Flayer? What is the significance of the grandfather clock for Vecna?