> Can you tell enough details for us to try to help you more efficiently?
> Like (1) what was the PSGML version you had installed before, (2) what
> exactly doesn't work -- show some file, tell how you try to use PSGML,
> and what happens that shouldn't?  Also, are you sure "M-x sgml-mode"
> invokes PSGML and not the sgml-mode that comes with Emacs?

… with pleasure!

The old psgml version, which is still shipped with openSUSE Leap
versions <= 15.4, is 1.3.2. The most recent version is 1.3.5.

The Emacs version shipped with openSUSE Leap 15.3 was 25.3.1.
The version shipped with Leap 15.4 is 27.2, and the latest version
that I got from GNU is 28.2.

emacs-25.3.1 with psgml-1.3.2 works.
emacs-27.2 with psgml-1.3.2 fails.
emacs-28.2 with psgml-1.3.5 fails.

When I run emacs-25.3.1 on one of my XML files, it indicates that it is
in the SGML mode ("SGML" written on the bottom line, SGML menu in the 
menu bar). Whether this an emacs-built-in SGML or PSGML disguised as
SGML I cannot say.

I attach an XML template for letters, which invokes some DTDs.
The DTDs should be stored in a directory named $ATXHOME/xml. The
editor should be invoked as "emacs -l cfg_emacs_aux.el doc.xml".

I suspect that the new Emacs balks at something in my cfg_emax_aux.el .

Regards,

Ulrich