Unable to answer "Does this bench have a backrest?" – Bench – https://osm.org/node/13511788838 via StreetComplete 62.2:

Just 1 part has the backrest (lol).
I would say, 2 benches:
1 bench, 2 seats backrest
1 bench, 2+1 seats, no back

Attached photo(s):
https://streetcomplete.app/p/325704.jpg