There are a number of altitude observation fields that you could add:
https://inaturalist.org/observation_fields?utf8=✓&q=altitude&commit=Search
or perhaps more properly altitude above sea level or elevation:
https://www.inaturalist.org/observation_fields?utf8=✓&q=elevation&commit=Search
Might be useful. I don’t see how anyone could use them to easily search for or select observations in a certain altitude range though.