Unable to answer "What type of barrier is this?" – Barrier (Unspecified Type) – https://osm.org/node/9693627911 via StreetComplete_ee 56.1:

Alley blocked off with wooden/chipboard 'construction' wall, has had mural painted over. From what I recall the alley was frequented by rough sleepers, so this was likely done by the council to 'wall it off'.