Closed captioning/subtitles not working with embedded youtube videos

My app’s URL:
I’m trying to embed a youtube video into my app which needs subtitles (captioning) in order to be instructive. To force captions we add: ?cc_load_policy=1&cc_lang_pref=en to the end of the url of the video. In preview mode, the captions appear, but not in the app itself (running in Brave). The captions do work/show if they’re manually enabled.