It starts with work being rather meaningless or just spinning wheels. It takes an enormous amount of effort to achieve little progress and even then the outcome doesn't bring about a great satisfaction, it is rather vague.
Which is then followed by cynicism. Which self-sabotages a way out, because with cynicism you'll be sure everything feels meaningless, even if it isn't.
Next, people grind through this perpetual state of deep unhappiness for the longest time possible, because showing vulnerability is taboo, plus bills have to get paid. Until the mind snaps, and subsequently the body.
Literally a countdown of your list: 3, 2, 1. Game over.
In the case of millennials, the link to work seems weaker. They seem to have a generic existential dread to them.