The term you're looking for is "shared culture".

Back in the day we always had a show or movie that we could share with our peers. No matter who you met, you could at least fall back to smalltalk about the Star Wars universe or everybody watched Friends or who would be the end of How I met your mother. Or spend the night discussing theories about Harry Potter lore. It was fun. Not anymore.

The last time I remember this was a phenomenon, it was Game of Thrones, I agree with the article there. We still got blips of it like Dune, Barbenheimer or maaaybe Stranger Things? But there really wasn't equally much to talk about.

Shared culture is fading out. Too much content. Everyone is watching completely different things. Shared culture is dying.