u/fool_hardie
It works system wide for all apps if you enable it from the Apple TV audio and video settings:
I tested myself with my own setup (Apple TV 4K first gen+ original stereo paired Homepods).
"Enhance dialogue in the currently playing video: Show playback controls, then select the Audio Options button and choose Enhance Dialogue from the pop-up menu.
Enhance dialogue for all videos: Open Settings on Apple TV, go to Video and Audio, and turn on Enhance Dialogue."