We are mostly going outside but do have one playdate friend that we do in a shopping mall a couple times a month if it's just too cold (so basically just a couple in January and we'll probably do a couple this month). I was skeptical at first but the mall is completely empty if you go first thing in the morning before most of the stores are open (it's just a few mall walkers and then employees trickling in to work). We all wear masks and let the kids play on a little carpeted area while we sit on the floor or on benches with them. It's about 30 -45 minutes and then we go. We social distance while we are there.
It's not ideal at all, but when we have a whole week of cold and wet weather like the last week, it has been good to have an option for just some brief interaction (both for me and DD, who is 2.5). This is the only indoor socializing we do and no one in our household has in-person work or school, so it feels as low risk as we can get for an indoor activity with people outside our household.