This directory does not exist and never existed.
So where should I look to remove it?
/etc/modprobe.d
grep -r nouveau /etc/modprobe.d
and make sure to recreate initrd after removing blacklist (mkinitrd). Blacklist file should be removed on driver removal, but it may stick around.
I’ve not downloaded nVidia rpms in years
In one of your threads you quite clearly listed nVidia repository.
How would I distinguish files in /etc/X11/xorg.conf.d/ that nVidia put there from others?
nVidia does not put anything there. Xorg works wit autodetection for years. Anything in /etc/X11/xorg.conf.d is exception, not a rule.
And finally, how do I force an install of the nVidia driver from the repository?
Post output of
rpm -qa \*nvidia\*
zypper lr -d