A study from the UK's Oxford Internet Institute (OII), which analyzed over 2.4M people globally from 2006-2021, found an 84.9% "positive and statistically significant" correlation between internet access and psychological well-being, compared to a 4.9% negative effect.
The OII, which analyzed people aged 15 and older, also found an 8.5% increase in life satisfaction for those with internet access, though the researchers noted that the results were not causal.
Modern technology, like anything, needs to be used properly. The happiest countries tend to be the wealthiest, and these (mostly Scandinavian) countries are happier largely due to their robust social welfare and healthcare systems. The digital world should be explored cautiously, not cited as the source of either happiness or discontent.
There are parts of the digital world causing wealthy Western nations to suffer mentally. As more children have grown up online, particularly with smartphones, they've missed out on historically normal childhood experiences, such as in-person play. The internet is negatively affecting people under 50, and corrective measures should be taken.