PeerTube has that built in. You can set up a channel and have it import or mirror a Youtube channel. For Lemmy there's several bots and scripts. As other people said that's what lemmit.online is about.
Be a bit careful when rolling this out. Several people don't like it. They've left Reddit for a reason and this is drowning them in bot activity. And usually these posts are low engagement, Reddit users can't see the comments, so you're not getting a lot of answers. I think it's good practice how we here have separated that to dedicated instances, so users can just have genuine conversations everywhere else.