iNaturalist does sort of offer heatmaps the way bouteloua pointed out before (in the original discussion) and also via the iNaturalist API. these heatmaps don’t always display nicely at all zoom levels, but it’s better than nothing, i suppose.
normalizing heatmaps seems to me like a relatively niche feature, and the methodology for normalizing seems like it would have to be customized quite a bit depending on your dataset and use case. so i’d be surprised if the iNaturalist staff devoted any time to normalizing heatmaps.
that said, you can get XYZ heatmap tiles from the API relatively easily and layer those on top of other layers that give you an idea of population. for example, in first screenshot below, i started with a dark base map, added a range map for American white pelican (in pink), and then put a night lights layer (which would give you a quick proxy for population centers) on top of that. the second screenshot is the same, except i added an observation heatmap for American white pelican.
i used QGIS for my example above, but you can use your own favorite GIS application, or you could even write your own map UI (ex. https://forum.inaturalist.org/t/which-gis-tools-do-you-use-and-why/3519/9). the XYZ tile references for the pelican heatmap and range map would be https://api.inaturalist.org/v1/heatmap/{z}/{x}/{y}.png?taxon_id=4334 and https://api.inaturalist.org/v1/taxon_ranges/4334/{z}/{x}/{y}.png, respectively. i got my night lights data from RealEarth (https://realearth.ssec.wisc.edu/tiles/NightLightsColored/{z}/{x}/{y}.png), but there are other datasets that could give you population or population proxies.
