How to link an object to a wikimedia image collection?

A recently mapped Castello di Rovere ruins was recently mapped with the tag wikipedia=Q55435447 This is going nowhere and when changing to wikidata= Q55435447 it informs there’s no label defined and but for an image there’s nothing on wikipedia. Opposed wikimedia_commons has a page loaded with many images.
Question to which the answer has eluded me is how can I tag this for the interested to get transported here? The wiki suggests it would be something like wikimedia_commons=Category:Castello di Rovere


yes, it works

though if wikidata=Q55435447 is present then it is already undirectly linked via Rovere Castle - Wikidata


And there I tried to upload the tag changes and low and behold, a conflict reported by JOSM. Of course a reader had to jump in just ahead of me. (Where’s my shake me head emoji).