This is how I do it: I only have one account on peertube.wtf. I usually discover content right here on Lemmy, in this community or in !peertube@lemmy.world. The channel directory is also a great resource for discovery.

When I click on a video that's not on my instance, I click Subscribe below the video, put in myusername@myinstance.xyz and click remote subscribe. It redirects to the correct place on my instance to subscribe/like/comment.

This way I've built quite a huge subscription list and have always around 30 videos in my watch later playlist.

When it comes to content discovery directly on PeerTube, I barely do it. Related videos aren't good recommendations most of the time. I tried the PeerTube Picks plugin for Firefox, it runs a local algorithm to recommend you videos. But I never discovered interesting stuff this way and it recently started to recommend me anti vaxx and other conspiracy videos, so I uninstalled it.

Are you sure they're only local videos? If I visit some instance like peertube.wtf it's mostly external videos both on the home page and the discover page. It's just that Peertube doesn't add the domain name to the usernames or descriptions in the feed, so they might look pretty much the same whether they're from remote instances or local videos.

I've been on Peertube for some time, so I have a good amount of subscriptions from all over the place. And I believe you should be able to subscribe to any channel, whether they're on a federated instance or not. As long as they're not blocked.

If you look up PeerTube instances dalek.zone has the largest number of videos.

Personally I use GrayJay. You can search and subscribe to them from there and they'll appear in a feed alongside your YouTube or whatever other platforms.

Care to give an example? Which instance and what are you looking for?

Also, it's normal to get different results: it's decentralised. If you ask your grandma and her network to find you a book about knitting and did the same with somebody else's grandma, it'll be a Venn diagram of results. That's how the fediverse works. Not everybody knows each other and not everybody wants to know each other.