I had the same issue as you but on a LG tv. To fix it I had to connect my Apple TV directly to the HDMI passthrough port of the soundbar and then the soundbar to the TV.
Connecting the Apple TV to one of the HDMI 2.1 ports of the TV also did fix the problem. When using the HDMI 2.0 ones, never got the option to enable Dolby Atmos.
I had the same issue as you but on a LG tv. To fix it I had to connect my Apple TV directly to the HDMI passthrough port of the soundbar and then the soundbar to the TV.
Connecting the Apple TV to one of the HDMI 2.1 ports of the TV also did fix the problem. When using the HDMI 2.0 ones, never got the option to enable Dolby Atmos.
Hope that helps