Unable to answer "What is the widest gap one can pass through here?" – Bollard – https://osm.org/node/5648602766 via StreetComplete 63.0:

Poller schützen nur Laterne. Pflaster generell mit Bordstein. Keine Ahnung was hier getaggt ist.

Attached photo(s):
https://streetcomplete.app/p/329904.jpg