the choice to display the “grid” style map rather than the “heatmap” style seems to be on purpose.
you can always create your own heatmap (see: https://forum.inaturalist.org/t/in-pursuit-of-mappiness-part-1/21864), or you’re welcome to use my map: https://jumear.github.io/stirfry/iNat_map?taxon_id=47532&view=heatmap&defaultzoom=3¢erlat=36.424¢erlng=62.104.
do you mean a choropleth? if so, you could look at https://forum.inaturalist.org/t/some-choropleth-maps-using-inat-data/21776. that thread contains links to an R script and also an Observable notebook that can help you generate state-level choropleths of species count. if you wanted to count observations instead, you could easily adapt either to get data from the API via /v1/observations instead of /v1/observations/species_counts. the necessary changes to generate county-level choropleths are a little more complicated, but if you’re interested, i can explain how to adapt either of these things.