One of the issues with trying to use iNat observations that way is that they’re not recording concentration/density of the species in question, they’re recording where people are going and what those people most often notice. There are lots of areas where certain species are very concentrated, but since iNat observers don’t go there those concentrations don’t get recorded. Similarly, in areas where people go they often do not record the most concentrated species in the area because they are common in those areas.
That said, you can play with the heatmap function, just replace the taxon id number with the one for your species in question: