Yes, those broad categories (also known as “iconic taxa” if you want to search for more info) are limited to a few common groups. Everything not in those select groups winds up under the “unknown” category (the grey leaf with question mark) in searches. There are a couple (rather old) feature requests to expand the list:
https://forum.inaturalist.org/t/make-crustaceans-and-myriapods-iconic-taxa/996
https://forum.inaturalist.org/t/create-iconic-taxa-for-bacteria-archaea-and-viruses/1464
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