how do you turn closed captioning off in Apple TV movies

If using a silver remote, press and hold on the middle button for a couple of seconds, and the audio and subtitle options for the movie should show up.

If using a Siri remote,

Swipe down on your remote's Touch surface to find the Info panel, then swipe right to see the Subtitles panel. Next, swipe down and select the option that you want.

More details here:

Turn on closed captions and subtitles on your Apple TV - Apple Support

I couldn’t get the triple-tap to work on the few movies with subtitles in my Library?

However, that got me experimenting a bit: If you quadruple-tap, the scaling is changed (zoom-to-fit), eliminating the letterbox bars at the cost of having the sides cut a bit. Any more tricks?

I also just figured a shortcut as well. If you triple tap the touch pad on the Siri remote without it clicking the closed captions will toggle.