According to this support article by Apple (Published Date: September 20, 2021).
https://support.apple.com/en-us/HT204069
"Your Apple TV and HomePod speakers automatically play sound in Dolby Atmos or surround sound if it's available with content that you watch. HomePod mini doesn't support Dolby Atmos. If you want to set up home theater audio with HomePod, find out how."
So no Atmos in Apple Music content in the upcoming software update (just lossless) and no Atmos when paired with an Apple TV 4K either, just stereo.
Perhaps given that the OG is now discontinued and Atmos content is growing in the Apple Music catalog Apple will launch soon a soundbar or a new speaker with Atmos support.
https://support.apple.com/en-us/HT204069
"Your Apple TV and HomePod speakers automatically play sound in Dolby Atmos or surround sound if it's available with content that you watch. HomePod mini doesn't support Dolby Atmos. If you want to set up home theater audio with HomePod, find out how."
So no Atmos in Apple Music content in the upcoming software update (just lossless) and no Atmos when paired with an Apple TV 4K either, just stereo.
Perhaps given that the OG is now discontinued and Atmos content is growing in the Apple Music catalog Apple will launch soon a soundbar or a new speaker with Atmos support.