Created attachment 768371 [details]
screenshot of yast

In pretty much every Opensuse and SLE that i have used there was the ability to
in yast under the /etc/sysconfig module in SYSTEM to change the default Windows
Manager and Desktop Environment.  Somehow this has disappeared between Leap
42.3 and Leap 15.

Attached is a comparison of Leap 42.3 and Leap 15 (as of late April 2018)

You can see in the 42.3 on the right there is the option to change the Display
Manager and that is omitted in the Leap 15 screen on the left.