Private worlds of other people now have a clickable button for making it your home, but it throws an error. Possibly because it's not possible server side and wasn't possible before in general. And so the button should probably be disabled just like on the stable version. Maybe also make private worlds visibly marked as private/non-public.

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ALSO:

You can now make instances of private worlds in-game, although only F/F+/I+/I ones, just like on the website. There's a chance this is not a bug but a new feature making it consistent with the website, but it's still worth pointing out as it wasn't possible before and it might be a problem of the button not being disabled just like in the problem above.