In https://www.openstreetmap.org/node/9873412245 I've gone with "amenity=bicycle_rental;bicycle_rental=dropoff_point" which seemed to be the best option from when this was discussed at https://lists.openstreetmap.org/pipermail/talk-gb/2022-August/thread.html#29221 , and seems to have reasonable traction at https://overpass-turbo.eu/s/1mm0 .