Puppy socialization extends much further than dog-dog play! Just like you want your puppy to be comfortable with collar grabs and hands on their bodies, you also want your puppy to be confident as they move around the world! Thus, let your puppy explore different surfaces with their feet.
Floors that are slippery, elevated, metal, make noise, move, etc., can potentially be scary for dogs. You can begin to mitigate that by exposing your puppy to all kinds of different surfaces now!
Depending on what you have available, give your puppy the opportunity to walk on carpet, hardwood, concrete, metal, tarps, foil, plastic, and more! The more positive experiences your puppy has with different surfaces, the better.