I’m still so surprised Disney+ degrades their content/streaming service so much. Of all the main services I’ve tried (Netflix, Prime, Hulu, HBO) Disney+ has some of the worst over-compression, lip-sync, and remembering-which-episode-is-next issues for me. Takes away from the “magic”.
Check your settings. I experienced the same until I altered Apple TV settings that fixed Disney+. If I recall, the setting was Match content or Match dynamic range (not near tv right now to confirm exact name)