Name the listening problem first
A conversation buried beneath background music and an explosion that is uncomfortable at an otherwise useful volume are different problems. Apple’s playback menu offers Enhance Dialogue to make speech more prominent, with Enhance and the stronger Enhance More. The latter can alter the original mix more noticeably. Compare the same dialogue passage before deciding which level is helpful.
Use loud-sound reduction for a different balance
Reduce Loud Sounds lowers the overall level by reducing dynamic range, so loud effects and music have less contrast with other sounds. It should not be described as a replacement language track or an audio-description narration. For an evening film, compare a quiet exchange and a loud scene at the same volume; judging only a title sequence can miss the problem you are trying to solve.
Add Isolate only when that stronger option is wanted
Apple’s current guide puts Add Voice Isolation in Settings, then Accessibility. Enabling it makes Isolate available within the dialogue feature’s playback controls. Apple describes substantial reduction of other elements of the mix when Isolate is selected. Treat that as a deliberate clarity choice rather than assuming that the original background balance will be preserved.
Distinguish a current adjustment from a default
Playback controls allow a change while watching; Settings, Video and Audio provides default audio preferences. Check which scope you intend before changing a shared television. Available controls depend on content, speakers or headphones and Apple TV model. If a menu option is missing, identify that combination rather than assuming every device running an Apple TV app has the Apple TV 4K box’s controls.
Questions, answered
Does Reduce Loud Sounds specifically select dialogue?
It reduces dynamic range. Enhance Dialogue and Isolate address speech prominence differently.
Is Add Voice Isolation itself the playing video’s final audio choice?
It enables the Isolate option, which is then selected in playback controls.