"Kids these days" says one of the UT dads, LOL.
I don't find the above to be true overall; I still see people holding doors and some folks, including teens offering up their seat on transit to someone elderly, and I hear plenty of please and TY.
The 00's, 90's, '80s etc etc. were not some panacea of very cultured, well mannered people living in harmony, LOL
And the 2020's are not an abomination of depravity. They are, however, one where we're dealing with new technology and socialization around that hasn't fully caught up yet.
Again, I think you're overselling this......
Worth adding, culture, including public behavior is always evolving. When we were growing up, construction sites were notorious for workers whistling and sometimes making lewd remarks at any attractive woman walking by. We rarely see this anymore. Said workers were rightly shamed; told that wasn't professional and wouldn't be tolerated on job sites, and over time, it has dropped off as a serious, normative issue.
Likewise, we can evolve how people communicate using phones, by some mixture of education, by parents, by schools, by peers, and by shaming where that alone is not enough. It will take time, but society has dealt w/far greater challenges, it can handle this one.