Unable to answer "What’s the surface here?" for https://osm.org/way/204493640 via StreetComplete 53.1:

It is very large stones (about 60x70 inches), made out of what appears to be concrete. I don't know if that should be marked as paving stones, concrete, or concrete plates.

Attached photo(s):
https://westnordost.de/p/156516.jpg