Hello,
It seems that with CentOS 7.6 and Gnome 3.28, a clean install of a Workstation package profile does not build the /etc/dconf/db/gdm.d/ directory tree. I have several desktops in operation which we kickstart built with an older 7.3/4/5 version of CentOS as the base install media. These all have a dconf directory for gdm, and I assume a dconf profile directory for gdm as well (though I admit it always worked so I never cared about looking for it). These existing machines are all running 7.6 today, and still have the /etc/dconf/db/gdm.d directory settings applied (like disable-user-list=true).
A newly built machine from the same kickstart but with 7.6 install media doesn't provide the gdm.d directory. I seem to recall, I admit it's been a long while, that with older versions of Gnome 3, dconf couldn't set things for gdm properly unless the settings were located in a special dconf db just for gdm. I can edit the kickstart %post% to make the directory(s) before dropping files in them, but I'm hesitant to do so if the files won't be honored because there's a more appropriate place now.
I can take this up with the gnome list, if necessary, but CentOS is my platform so I'm not sure if it's a distribution specific configuration or functional change to Gnome. I tried searching through gitlab.gnome.org to see if I can dig up any issues, release notes and such, but I didn't find anything that seemed relevant.
Thanks!
--Sean