Like most answers about the US, it depends on a lot, we’re a big place. As someone who is at the movies 3-4 times a month I’ll say the biggest factors that contribute are

• When you’re seeing the movie
• How new/popular the screening is
• What movie you’re seeing
• The chain you’re at

I typically go during the week after work and generally wait a bit to see new releases and I usually have a couple other people with me in the theater and they’re usually chill. If you go opening weekend to a new movie in a crowded theater then I’d say you can pretty reliably count on a few people making quietish comments and a few people checking their/phones a few times. I also find if you tell people to shut up or put their phones away they usually listen. I’ll also say if you’re going to see the new prestige A24 drama expect less interruptions than say The Super Mario Galaxy movie or The Minecraft Movie