Speaking of which, I don’t get to experience quiet theaters anymore because of all the ads they play. When I was a kid/teenager, theaters only played movie trailers before a film. Maybe they might have some film trivia running before trailers start, but that was it.

In my youth I worked at a movie theater. The trivia questions and answers (as well as the lobby card photo pictures from famous movies displayed between questions and answers) were on slides. There was a separate projection window where the slide projector displayed on the movie screen. Yes, we'd very occasionally forget to turn off the slide projector when starting the movie projector, so you'd see both on the screen for a second until the projectionist realized it.

The theater was quiet and peaceful while you waited for your film to start.

You're right about the quiet part. Almost like a church or a library. People sitting next to one another in the theater waiting for the movie to start would talk in hushed tones. The only exception to this was hugely popular midnight release movies where its a whole theater full of fans of the movie talking loudly in excitement with the shared experience of fandom. There was a really cool welcoming electricity where everyone was on equal footing and just excited to be seeing the movie with each other, friend or stranger alike.