i don’t have an iPhone and i haven’t used the new app, but it seems like historically, the iNat apps have just piggybacked on the phone’s default camera and audio recorder. Apple is reputed to have a very good audio encoder, but without having access to the the original file on the device, it’s hard to say whether the possible cutoff in higher frequencies was present in the original recording.
it is known that when an M4A file is uploaded to iNat, the server reencodes it, and that is a point where audio problems also could be introduced. see https://forum.inaturalist.org/t/issues-with-quality-of-sound-recordings/52178/22.