I am a millennial, and will generally defend my generation. That said, one of the criticisms of the millennials (and I presume zoomers as well) is that they have been utterly poisoned by the overuse of irony in pop-culture. They're a product of the late-stage artistic stagnation the major entertainment mediums are locked in, so their entire cultural frame of reference is genre subversion and deconstruction. Everything is "post"-something, and the dreaded "genre trope" is a bogeyman to avoid at all costs. Far too many younger players are positively allergic to sincerity, and are basically too insecure to play a character straight in a roleplaying game. They have to try and be the class clown and show how cool they are with their "quirky" ideas.
That said, don't be a doomer about it just yet. If you're willing to take up the GM-ing torch, some of this can be overcome by good leadership. First of all, don't run 5e. And I don't say that for any game system reasons. 5e is by design a game with no strong theme or tone of it's own. If you instead run something with a strong internal tone, like say Cyberpunk, Deadlands or Call of Cthulhu, you might be surprised at how willing even younger players are to fall in line with it. Generally speaking, GMs have a lot of power to set the tone of a game and players are likely to follow. For my Roll20 games I have a "table rules" post I put out with the game listing, and the first item is "play sincerely". I make it very clear up front that I have no time for joke characters or people who play ironically, and generally I get agreement with that from across generations. A lot of younger people are desperate for some sincerity in their entertainment, even if they don't consciously realize it. When players do try to get "quirky" I have NPCs react the way real people would, with eye-rolling and irritation, and treating them like children. When the overplayed joke starts to fall flat, people usually stop it.
Be quirky in return.
Play a human fighter with a wife, kids and extended family to support. He’s adventuring to get his family a better life. He has no interest in the other characters’ drama; he’s here to provide for his family and drama gets in the way of getting the job done so he can home and see them (also insist on plenty of downtime for precisely this reason).
A lot of the 5e groups I’ve experienced won’t have any idea what to do with that. It will (sadly, not literally) break their brains.
Yeah, I've done something similar in the past. Play a straight-laced, well-meaning, mature character, and play that character as intelligent and capable. The irony brigade can't deal with a Dudley Doright character who isn't being played as a joke. They'll try to make fun of you for a bit, but it won't work because your character exposes all their childish insecurities. You'll end up having to play the party's dad initially, but you'll also end up being the de facto leader, and after a while they'll start falling in line.
EDIT: You do have to be a little bit careful with this approach. Playing a realistically good person is way more difficult than playing a self-serving dickhead or a stereotype. I have seen people try this and fall horribly flat because they aren't good leaders. Trying this approach and failing is one of the reasons for the "lawful stupid paladin" stereotype.