There's also the mental state of the world report by Sapien Labs, which tells a different story: https://mentalstateoftheworld.report

I believe this is more accurate, although it's not just happiness. They measure MHQ, i.e. Mind Health Quotient with various mental health related metrics.

I just looked at the report for the first time and it's quite insane how bad young people are feeling globally. Old people seem to be fine on average everywhere. The distributions don't even overlap i.e. the most unwell old people (Ukraine, UK, etc.) are doing better than the most well-being young people (Nigeria, Tanzania) on country average basis.