The evidence given that it is a trend, pre-show prods to turn off your phone, feels like it has been happening as long as personal cell phones were a thing.
https://theface.com/culture/why-are-theatre-audiences-gettin...
Just one of many reasons going to movies isn't really worth it anymore, unless you're really in the mindset you want to go and having lights shining / jostling around in your peripheral vision won't annoy you.
We see movies a couple weeks after their release and go mid-week (a 7pm-ish show after I’m done with work). Often the theater is empty. When there have been people nobody used a cell phone or did behavior that was distracting. (BTW bringing a 4yr old to the movies usually means we are the annoying group, like when my daughter singing the songs in the Little Mermaid.)
So my guess is that this behavior is likely limited to opening weekends at popular movies where telling someone you were there by posting a photo on social media is part of the experience for them.
Circling it all into just "kids these days" type discourse is pretty reductive and reddit-brained, I think.
On a tangent, those two are titles that i'll never see even if they stream on something i subscribe to, because the enormous hype has completely put me off.