I think the first part of this misses the point of both money and happiness.

The ultimate goal of any life form we are aware of here on Earth is proliferation of the genes it carries, whether that be by individual longevity, reproduction, or longevity and reproduction of closely-related individuals that carry the same genes. Emotions seem to have evolved as a means of motivating behavior toward better adaptive fitness, in an obviously imperfect way because the system has nowhere near perfect information. Maybe you can broadly class emotions and motivations into good and bad or reinforcing versus dissuading, but not all good or reinforcing emotions are happiness.

Simply put, people act with other ends and this includes acquiring money for reasons other than to become more happy. For some reason or another, at least since Aristotle there seems to have been this widespread assumption that all other motivations are only intermediate motivations and happiness is the only terminal motivator. We want power because it will make us happy. We want security because it will make us happy. This seems obviously false to me. I personally do and observe others doing many things that I know will not make them or me happy and I don't think these are wrong or dysfunctional behaviors. Many of the successful people who ever lived were not happy. Michael Jordan and Kobe Bryant were perpetually pissed off and miserable. Look at Lamar Jackson before and after the Christmas Day game with the 49ers. Before the game, he complained to the press that the Ravens were being overlooked and deserved to be favored. They win and everyone is now rating them as the best team in the league and he responds by saying he doesn't buy it and thinks they proved nothing. What gives? He obviously needs some chip on his shoulder for motivation and it doens't matter if his reasoning stays consistent or sane. Win or lose he'll be unhappy because he needs to be unhappy to win. Happy people don't obsessively fixate to the point of alienating friends and family on an activity that damages their own health and longevity. Winners do. Happiness is not the end goal here. Winning won't bring satisfaction. Winning in itself is the terminal motivator.

Money works the same way. Elon Musk and Jeff Bezos both hope to grow more zeroes at the end of the bank accounts in part because they want to fund moonshots but also just because of a primeval dick-measuring instinct to be #1 at everything they ever try to do, because genes in human males of the past that induce that kind of behavior produced men who had a lot of children and killed other men's children. Why does the money not make them happy? Because if it did, they'd have stopped making more of it hundreds of billions of dollars ago after they finished satisfying all of the reasonable human needs and desires that are more specific than "be better" and "do more."

Money is nonetheless positively correlated with happiness because, as they say, having it means you can buy stuff. Some things you can buy include better health, better security, better education and housing for yourself and your family. These happen to be things that remove particular causes of unhappiness, but they don't remove all of them. Some of them can't be removed. Some people are unhappy because of irrational brain states induced by pathology and nothing that be bought given today's understanding of neurology and psychiatry can ever change that. But some sources of unhappiness aren't removed because not all sources of unhappiness are bad things that the money-owner wants to remove. These people don't want to be happy. They want to be great. They want to win. No matter how much greatness they achieve and how much they win, many if not most will never achieve enough because if such a thing was even possible they would never have been as insanely motivated to achieve what would have been enough.

This is nothing to do with human psychology. This is a far more basic fact common to all life. No amount of profliferation is ever "enough." The pithy Agent Smith nonsense about non-human, non-virus life reaching a natural equilibrium with its environment is not true. All life will consume all available resources and then look for more. The reason temporarily stable ecosystems exist is because predator-prey population dynamics and competition between predators keep any single population from ever becoming too successful, not because it doesn't want to be more successful but because external constraints stop it.

This is exactly why we recoil from fictional tales like Brave New World, think of wireheading as a bad thing, and socially discourage heavy consumption of euphoric drugs. Some part of us instinctively understands that happiness isn't the point and can itself be counterproductive because we need some amount of unhappiness to stay motivated to do what we are actually here to do, which isn't be happy. Yet we still see research projects like this attempting to explain why people living with abundance are not happy. The only reason abundance exists is because no amount of it can ever be enough.