The best challenge is to get yourself some Linux distro that, after installing, just drops you into a shell and then install and configure the server software or the desktop software yourself. You could use a Raspberry Pi for this.
I used arch btw.
Usually users can post from any instance to any federated community on any server.
Unless the federation between lemmy.ca and Lemmy.ml is wonky/broken, one of the servers is overloaded, or they've explicitly forbidden it, you should be able to post there.
@Ediacarium
@feddit.de