To me, happiness is related more to gratitude than to intelligence. You could have very little and be happy and you can have a lot (money, friends, autonomy) and be miserable. The modern world has a lot of stressors but also a lot of things to be thankful for. It's the best time to be alive for humans so far.

Good example of gratitude: https://gwern.net/improvement

This is exactly how it is, writing from Finland that has been selected The Happiest Country in the World for who knows how many years in the row now.