Thanks for everyone who replied!
At first, I just copied the "cat" output of PTrenholme post
into a newly created file
but then it occured to me to look better in the directory
to which few "*.service" links are pointing and I saw "gdm.service"
and "kdm.service" files. So I removed the created file, did a link
ln -s /usr/lib/systemd/system/kdm.service display-manager.service
rebooted ... and now I have the KDE graphical login.
To paraphraze "THHGTTG":
"There is a theory which states that if ever anyone discovers
exactly what the Fedora boot sequence is for and why it is here, it will
instantly disappear and be replaced by something even more
bizarre and inexplicable.
There is another theory which states that this has already