Big Sur Subtitles English -
: Click the "+" (plus) button to create a custom look, where you can adjust the font, size, color, and background opacity. Feature Highlight: Live Captions
To enable or customize subtitles, use the Apple Menu Captions Settings : Big Sur subtitles English
If you are using a version of Big Sur that supports it, or have updated to more recent macOS versions, you can use Live Captions . This feature provides real-time text for any spoken audio on your Mac, including FaceTime calls or web videos, regardless of whether they have pre-made subtitle files. How to customise subtitles and captions in macOS 11 Big Sur : Click the "+" (plus) button to create
: You can also toggle "Show automatically when languages do not match" to have subtitles appear only when the video audio differs from your system language. Visual Customization How to customise subtitles and captions in macOS
: Choose from Default , Classic , Large Text , or Outline Text .
: Check the box for "Prefer closed captions and SDH" to automatically show English subtitles whenever they are available.
You can change how subtitles appear to make them easier to read. According to AbilityNet , you can choose from several preset styles or create your own:

