Not sure if it’s been shared on this thread or not but this tool created by Elias Pschernig is a quick way to find your rarest observations:
https://elias.pschernig.com/wildflower/leastobserved.html
^^^This was shared on another similar topic that I was looking at just a couple days ago: https://forum.inaturalist.org/t/rarest-finds-on-inaturalist/16195/94
My rarest animal I have ever seen (at least by iNat standards) are these Chionomus herkos planthoppers, of which I hold the only 3 (tentatively IDed) observations on iNat: