I’ve noticed this shift too in my decade+ in the US. It’s actually really nice to learn someone else noticed it too, because no one I’ve mentioned it to has known what the hell I'm talking about.

I think I only heard in it in some African American English accents when I first came here, but now it’s common among younger Americans more generally. I’ve also heard it applied to other consonants - you can replace quite a few of them with a glottal stop and still be understood :D