Lots of things! Here are some things I wouldn’t have nominated 5-7 years ago, but can work now.
I’ll be brief, and not talk about caveats about each thing. I don’t want to type that much and you don’t want to read that much.
A picnic table can be eligible, if it looks permanent (check the grass under the seats) and like a great place to socialize. (Even tho the table itself is mass produced - a picnic area is a place to be social.)
Neighborhood/apartment amenities (playground, pool, clubhouse, etc)
Park/trail rules signs
Restaurants are easier to get thru
Coffee shops, tea shops, and bakeries seem to sail thru.
Breweries, if you emphasize the social nature (like cornhole) or if they have art
Event venues
Bulletin boards / kiosks with changeable event notices
Any workout gym, even a chain, or in a hotel
A swing or something that’s not a full-fledged playground, but is the only public access play piece around
A generic bench that anchors a trail or viewing spot
You don’t HAVE to have a man-made sign for everything, altho it helps. For example, you can show in a picture that it’s a volleyball court.