I have tried everything.
This is what I’ve found.
Video files on my NAS with 5.1 audio or better produce the most awful audio sync problems on my system.
If I set the ATV to output Stereo only the sync is fine.
If I change the audio track on video files that have the option to a 2.0 audio track the audio is fine.
All other apps such as Netflix, Prime & Apple TV+ work perfectly with excellent sound quality.
I have tried turning on and off Match Frame Rate and Dynamic Range(as suggested on another thread) to no avail.
I have a Yamaha AV Receiver that receives HDMI ARC Audio from the TV which is fed HDMI from the Apple TV.
I could not get the TV to receive as good an Audio/Video combination by routing the ATV through the Receiver to the TV. All the 4K goodies get dropped (I think)
This is driving me nuts as I’m sure this problem hasn’t always existed.
All OS’s and versions are bang up to date.