Verify that your HDMI cables are rated for a bandwidth of 18 Gbps or 48 Gbps.
Verify your HDMI output settings on Apple TV to be YCbCr (not RGB) and start with Chroma 4:2:0.
If you get HDR 60Hz, then that is for HDR10, not Dolby Vision. Dolby Vision would be specified on Apple TV, if detected to be supported by the other equipment.
For more verification and options from us, please specify the model TV and model soundbar.
For passthrough of Dolby Atmos audio from Apple TV, the TV needs to have an HDMI-eARC port. I expect that one HDMI port on the TV would be marked ARC or eARC. TV HDMI ports may need configuration, depending on brand and model.
For passthrough of 4K Dolby Vision video, the soundbar needs HDMI 2.0 or 2.1 ports with HDCP 2.2 or 2.3. See its manual.
If neither the soundbar nor the TV allows for these high end passthrough options, the you may want to consider a third party solution for exactly that: HDfury Arcana.