That's exactly the problem: a joke works once, twice max before everyone knows it by heart. Avocado toast and millennial depression were funny around 2016-2017 because it was new and it touched on something real. Now it's become this thing people repeat mechanically, like you're scrolling through a machine that spits out the same content on loop. Algorithms don't help either, they push what works rather than what's original.
You're right to point out that the focus has shifted. Gen Z became the easy target now - jokes about TikTok tics, the way-too-much thing about triggers, all that. So millennial memes just hang around like wedding jokes from 2004, nobody adds new ones because it's not the trend anymore. It's not that you're getting old, it's just that humor cycles through so fast on social media. Six months ago everything was funny, now it's dead because everyone got the same joke at the same time and killed it before it had a chance to develop a bit.