Game nights, potlucks, and other house glue
Choose gatherings that are easy to join and easy to leave. A card game, a potluck, a movie, a walk, or a shared errand can work better than a large planned event.
Keep the burden shared. Rotate hosting, make spending optional, and include people with dietary, schedule, or social limits. The point is participation, not performance.
If one event flops, do not force it. Try another format. House glue works when it fits the people actually living there.