That’s not really possible because there’s no way to know which instance to direct someone to. No point directing them to an instance where they don’t have an account.

At least they will know it is on lemmy , then they can figure out how to use it. And that's a general problem of the fediverse, there are extensions that redirect you to your home instance for that.

Also I don’t think showing buttons like upvote which just redirect to another page is a good UX at all.

I think it is at least better then the current state, where you have a tiny button that testing with heat maps will probably show is almost invisible, maybe adding text "go to lemmy to participate in the discussion" is also a decent option.