I don’t use the iNaturalist app at all, usually. I track my location using a phone app specifically for that; it makes a GPX file, basically a line tracing my path on a map. Then after I’ve moved the photos off my camera to the computer, I use another program to sync the photos to the GPX track, based on the photo’s timestamp and where I was at that moment. This saves a geotag into the photo’s file, and so when I upload to www.inaturalist.org, the location data is automatically filled in.
This is the fastest method I’ve figured out, but it’s not without perils. Quite frequently something will go wrong with the process: I forget to start the location tracker, I forget to save/accidentally delete the location track, strange things happen with file programming, my camera date/time is set incorrectly and won’t match the track…very rarely the photo files will get corrupted while being geotagged, but that’s not horrible if you have the originals still on your camera card.