My problem turns out to be a software issue to be resolved with the next TVOS update.
Mine is a video problem applying to Apple TV 4K models, under Settings > Video and Audio > Match Content.
There are two options with this setting, Match Dynamic Range and Match Frame Rate. The problem exists with these to settings switched to On. The problem is resolved by switching these two settings to Off.
As far as I know, this problem/solution only applies to Apple TV 4K (1st Generation) models running tvOS 16.5 (20L563). I also own an Apple TV HD model that plays music videos correctly with Match Content settings set to On — that is how I isolated the source of the problem.