setenv DISPLAY <host>:0.0

In the old Version 4.x.x under SuSE_13.2, the System Settings granted 
the possibility to

         setenv DISPLAY <host>:0.0

which was useful for opening remote programs.

As a preparation, there where sufficient some slight modifications to
         /etc/X11/xinit/xserverrc
         /etc/X11/xdm/Xservers
         /etc/X11/fs/config
which consisted in removing the "-nolisten" or "no-listen" parameters.

Now, in the new Version 5.x.x under Leap 15.1, the environment variable 
DISPLAY can still be set.  But the above modifications are no more 
sufficient because the system continues to complain

         <program>: can't open display <host>:0.0, aborting

not only at the trial of opening a remote program, but even with a local 
program.

How can the useful functionality of "setenv DISPLAY <host>:0.0" be restored?

Best regards,
Wolfgang