Money can't buy happiness, but it can buy less unhappiness. There's diminishing returns, of course, but I'd hazard it looks a bit like ln(n), in that the returns are quite significant in the beginning.
The terms I've learned to use is rather: Happiness, and Stressors.
If you need your car to earn money, and you don't have the money or other resources to repair it if it breaks - that's a huge uncertainty and a huge source of stress and worry. Liquid funds can remove that source of stress. More drastic examples would include rent or food.
That's why liquid funds can remove impediments and distractions from your life, but once all of those are gone, then what?
And the remaining unhappinesses can end up in starker relief, as you continuously try to remove all unhappinesses from your life to nearly impossible and sometimes distorted degrees.
The problem isn’t that money doesn’t buy happiness, it’s that it can remove your ability to endure the necessary amounts of unhappiness in life.
Money can very much buy happiness. Most of the things that make you unhappy can be remedied with money. How much money you need to accomplish that depends though.