If you follow a PeerTube account from Mastodon, the videos appear in your feed and you can interact with them just like you would with any other post. For example click on @helenmclaughlin
Was there a particular thing you wanted to do that felt workaroundish?
About PeerTube instances, the videos they show on their own site depend on what the admin wants to do. Some of them just show local videos, some show entire other instances, some show just particular accounts.