The yt-dlp project uses Deno as its default and preferred JavaScript runtime when downloading YouTube videos (this replaced their own handwritten JS interpreter). Fortunately yt-dlp also has support for Node and QuickJS as well as deprecated support for Bun, but I don’t think any of those were preferred by the project for various reasons such as portability, security and I think also speed.
See https://github.com/yt-dlp/yt-dlp/issues/14404, https://github.com/yt-dlp/yt-dlp/issues/15012, and https://github.com/yt-dlp/yt-dlp/wiki/EJS.