You can use this page as a catalogue btw: https://grayjay-sources.github.io/
However, as overarching and as big as Youtube, there's none, so you'll have to contend with nicher platforms for niche subjects. Like e.g. for Youtube Shorts-style videos, Odysee, Loops or TikTok.
Loops btw, isn't supported on Grayjay yet, but uses ActivityPub, meaning you can follow users from Mastodon, Mbin, Misskey, etc.