This might be related to Apple, normally Apple is very good for accessibility, but even the BBC has challenges with subtitles on AppleTV, same with the Dutch NPO TV:

“Why are there no subtitles on BBC iPlayer via Apple TV?

There are technical challenges associated with delivering subtitles to Apple TV which will require a significantly different solution to that which we use on all other platforms. We are working towards it but don't currently have timelines associated with this support.”

Source: https://www.bbc.co.uk/iplayer/help/questions/accessibility/a...