While you're at it, could you also change YouTube so that captions being on/off is a per-language thing and not a "The user turned off subtitles for language X, therefore it's the only they speak, therefore let's turn on subtitles for all other languages." thing? It's really annoying that whenever I watch a video that has a language different from the previous video I watched, the first thing I have to do is to turn off the captions.

This isn't a proper solution, but if you watch with yt-dlp+mpv, you can configure default audio and sub languages in mpv (globally) and they will also work for YT videos in addition to your movies and such. Plus if you do toggle them on/off for one session it won't mess up your mpv config.