Frequently Asked Questions | Bandcamp "We don't do any audio processing to your uploaded files except whatever's necessary to fit into the download format. For example, for MP3 downloads the audio is resampled to 44.1kHz. FLAC downloads on the other hand are bit-for-bit identical to the audio you upload, all the way to 24/192."
So the ideal is to upload from full-res (whatever that is in your situation) for FLAC downloads.
Then ask Apple to at least offer the choice of ALAC downloads from the iTunes store, made from the 24 bit sources they've been requesting and getting.