an activity which brings people together, including such which don't yet know each other, repeatedly, often but not required to be in person, where the people have to socially engage with each other, where there is peer pressure to not just skip it all the time because it will cause issues for others
that helps with loneliness
that it gives a framework of expected interactions and often a context where unusual but not mean actions do not or at lest much less lead to social embarrassment helps too
but here is the thing, to some degree this was/is true for a lot of traditional activities where you e.g. join club, association or similar. With the main difference being that such traditional clubs instead of being very lax/welcoming for people which are a bit socially awkward often had quite strict behavior codes. To some degree this helps people which are just not good at socializing and need some guidance to to fit in, but also often comes with all kinds of issues (like hazing rituals, or a much high chance of you not fitting in at all)
anyway my point is it doesn't have to be Pen and Paper and even less DnD, it can be all kinds of "meetup with soft peer pressure to show up" situations like
- a weekly board game meetup (especially for long running games like Gloomheaven)
- a wow guild
- some team sport clup thing (but not all, in some you just do thing alongside of others which means the extrinsic motivation to not skip it is much lower)
A main issue I see here is that a lot of the things can work over internet, but work easiest if there is a physical local close by meet up point. Like a board game store, game cafe, sport clup house, etc.
But not only has that gotten much harder due to the combo absurd high rent prices making new places hard and COVID having killed many existing places. But also the way the US seems to be doing zoning in many states (i.e. separation of where everyone lifes and where out of house life can happen) seems to be very hostile and many other things common for socializing in other countries