Play it mainly on Discord nowadays, is really fun imo. As for it becoming mainstream, I have no issue whatsoever. In fact, I think this change is good, as more people means more players and potential dms, and more potential characters to see get made and the like.
To the comment above, Dungeon and Dragons is a roleplaying game where you make a character with certain stats and, with a group of other players and one Dungeon Master (who is like the narrator who controls all the NPC, enemies, etc.) you sort of talk out an adventure. I have not watched Stranger Things, but from what I can tell they do it similarly to how some play the game. Some play extremely into it with Live Action Role Play where they dress up as their characters and the like, while others are extremely casual (aka all theater of mind slash imagination). If you want to see how the game is in action, I recommend Critical Role streams. A group of voice actors from various places playing DND, usually DMed slash hosted by Matt Mercer. There are also tons of Youtube channels like Runesmith, XP to Level 3, Davy, and more if you want to look into what it is like to play DND.
In summary (lol): DND is a game where you play pretend with your friends under a certain set of rules, with one of said friends being the narrator to an overarching tale (or short one) that you and the other players go through in the metaphorical shoes of your character. Hope this helps.