Apple recently updated its Apple Music support page to clarify the compatibility of Dolby Atmos (recently introduced) through Apple mobile speakers.
List of Dolby Atmos compatible Apple mobile devices
• iPhone XS and later (except iPhone SE)
• iPad Pro 12.9 '' (3rd generation and later)
• iPad Pro 11 ''
• iPad Air (4th generation)
100% compatible with AirPods, AirPods Pro and AirPods Pro
Entry-level iPads, iPad mini, iPhone XR and iPad Air 3 have therefore disappeared from the list. only applies to speakers, and that Dolby Atmos spatial audio works with any device as long as you use AirPods, AirPods Pro, or AirPods Max headsets.