I just realized that in that Debian Stretch system,
I HAVE NO /home/<user>/.gconf directory !
[ While I have one my laptop using Ubuntu 14.04, also on my old desktop
running Debian Lenny]
but it didn't rebuild itself so far !
What should I do to get it rebuilt ?
Bernard
It'll rebuild itself when it's needed. The lack of a .gconf directory is probably not causing your problem; rather, your problem is causing the lack of a .gconf directory.
What happened when you tried running tasskel and installing a simpler Windowing setup?