I think this would need a property mapping a contest with the used identifiers (basically, that table but in wikidata form).

So for instance,"Wiki Loves Monuments 2021 Sweden" could be defined as including the "listed building in Sweden (Q328070)" and the "listed historical ship in Sweden (Q16501309)", which use P1260 and P2317 identifiers respectively (whereas a few years earlier, maybe only Q328070 were included).