They’ll never have the full Mastodon functionality because they’re Facebook. It’s always going to be a one way proposition where Masto can see them but they can’t see us. It’s honestly kind of like being a creepy Peeping Tom.
Assuming, of course, that your instance doesn’t block Threads. Many (most?) do. Some even block second-degree connections.
https://kbin.social/u/@potus@threads.net you can follow him via this link (anyone else on other kbin instances, just adjust the link to your instance, assuming you aren't defederated or if it isn't bugging out atm on your server it should work)
Remember that federation is currently one way with threads. You and other fediverse users can see your own replies and boosts etc on their posts and interact with each other, but no one from threads can see your interactions or replies to them.
If you search for @potus he comes up and you can select Follow. Content should then show in the ‘Microblog’ stream. Might take a while to start flowing, though