Launching graphical applications without $DISPLAY


my network has two hosts, each one of them can access the other using
"ssh -X" being both client and/or server at the same time.

Everything works fine and the graphical applications can be well launched
as long as the shell environment doesn't contain $DISPLAY, because ssh -X
sets its own "localhost:10.0" together with everything else which is
needed for X forwarding.

However, apart from ssh sessions I cannot launch any graphical
application from virtual terminals without $DISPLAY, even though they can
still be launched from the desktop environment menu.

How is possible to launch a graphical application without (apparently)
setting a $DISPLAY variable?

And how could I launch them as well from terminals without $DISPLAY?

Thanks in advance for answering.

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