Right now, go to pixelfed.org and there's a "Join" button in the top right corner, click on that and there's a message telling me "To join Pixelfed, you need to pick an instance. You can find a list of instances on the sites below." - click on either of those and it's a completely baffling list of stuff with no obvious way to continue. At this point I always give up.

Hah, you're right, you end up in some slow-loading dashboard (hooray fancy graphed realtime numbers!). I clicked on a random hostname, it's another dashboard page with the hostname in large, the same hostname as a link as a subtitle. I clicked the link, and hey, it's a page that looks like Instagram's sign up page, with the difference being that this one says:

"Registrations are closed."

I tried a few more sites, even the one with the most number of users, and they all say this. Only the 5th site I clicked on allows me to register.

Ah only now do I notice the column "Open Signups" in their fancy dashboard...

That being said, it's open source, so there are hacks to make your stream public. But they're hacks, and you're not going to get that out of the box.

You can even follow me from your instance. You can't get more public than that.

Having said that, it still requires a bit of hackery. There's no way to get rid of the home/landing page if there's the one user account, so you have to do a bit of php/apache/nginx/whatever magic to redirect past it to your user timeline.