Which content/information sites dependant on javascript can be found? I always find marketing oriented or app interaction heavily using js and thus unable to archive...but otherwise...

Literally any modern social media, YouTube comments, anything using client-side rendering frameworks

I don't see Youtube/IG/Fb/Tiktok comments as valuable content or information, I would be surprised if somebody is treasuring such content.

Maybe tweets, but APIs are available for archiving (more or less).