Also notifying @[email protected]
You can cross-post by clicking this button of two squares, with one on top of the other.
This will lead you to a menu where you can change the content and title of the crosspost and select a community to crosspost to.
The onion link (http://zlibrary24tuxziyiyfr7zd46ytefdqbqd2axkmxm4o5374ptpc52fad.onion/) has never stopped working for me. I think it should be the most reliable way to connect to it.