Incorrect.
The entire point of Dolby Atmos is that it’s adaptable, meaning no matter how many speakers you’re listening to it on, it’s still a different mix than the stereo mix.
Even on stereo speakers, it’s a different mix, usually done by a different mixing engineer, using the original multi-track tape or whatever kind of format it was stored in at the time.
Even on stereo headphones and stereo speakers, you are still not listening to the original stereo mix if you have Atmos/spatial audio enabled.
It was my understanding, though, that Apple Music’s support for Spatial Audio is a vendor specific thing limited to Apple audio products. If you’re listening on non-Apple devices (such as a 3.5mm headphone jack), I don’t think Apple Music is delivering the Spatial Audio version (mixed down to stereo in any way). It definitely doesn’t support the 3D sound stage aspects of Spatial Audio without head tracking or the HomePod line’s speaker arrays.