All of the replies so far are suggesting ideas for an individual but seem to be missing the real crux of the matter...

Yes, you'll be less lonely if you join a group, get out of your house, etc... But how do we actively incentivize that? Social media and whatnot have hundreds of thousands of people working around the clock to find ways to suck you in and monopolize your time.

While "everyone should recognize the problem and then take steps to solve it for themselves" is the obvious solution, it's also not practical to just have everyone collectively decide they need to get out more without SOME sort of fundamental change in our society/incentives/etc