You can participate, but it’s such a hassle :-/

1. You find a post on <foreign instance> (because the feed on your small home instance is very limited) and just want to upvote it.
2. You get to the login screen and remember that this isn’t your home instance.
3. You open your home instance, navigate to the search form.
4. You try to find the link for the original post that you can enter in hour home instance’s search bar (which isn’t at all easy to find if you don’t know where to look).
5. You paste the link in your home instance’s search form.
6. You open the post on your home instance.
7. You vote.

This is frankly unacceptably complicated for a regular, casual user to just cast a vote on a post.