Add subtitles to the entire video
After creating and previewing your content, click on Generate
Toggle the button next to Add subtitles
Some scenes are not subtitled in my video
In case you have turned on subtitles, but added new scenes afterwards, the new scenes don't have subtitles by default.
Switch subtitles off and on again to apply subtitles for the new scenes. You can verify how many scenes have subtitles by hovering over the ℹ️ info button next to the subtitles switch.