Ask Dad

Invite them over. Have dinner, drinks, hang out, do stuff you like to do with them. Watch sports, or a movie. Listen to music. Grilling is a good outdoor excuse to wave them over.

But keep in mind, proximity doesn't necessarily make for good friends. You might not enjoy the same hobbies or foods or whatever. You may not enjoy each other's company. Worse still, you might have different feelings about hanging out than they do. Are they close enough that you'd feel obligated to invited them to everything?

It's best to invite them over a few times, but maintain boundaries.

not a dad, but someone co-living in an apartment with 7 other people

took me over a year of being a shut-in to start talking with them, and after a few months of connecting, told em i was a shut-in, but am now glad that i started talking with them, and they just accepted and respected it and that's all

people don't care why you haven't initiated contact for a year, 3 years or a decade of being neighbors, all they really care about is the first "sup, hi" and how it goes from there

so, just, greet them and when you see they have time start a conversation. the rest will follow.