Ciao vmicho
I just passed https://www.openstreetmap.org/way/1171316488/ today by bike.
In my opinion this is definitely not a retaining wall retaining bare rock.
In my opinion this island in the roundabout should be mapped as traffic calming island, as described in https://wiki.openstreetmap.org/wiki/Tag%3Atraffic_calming%3Disland and https://wiki.openstreetmap.org/wiki/Tag:junction%3Droundabout#
Greetings,
habi