In Linux world, there are changes occurring to replace X Org with Wayland. Most of Desktop Distributions are getting shipped with Wayland as default session for GUI instead of X Org.
In a Wayland Session, DB2SETUP GUI is not working. It looks for DISPLAY Variable and fails. Even if you set Display Variable to :0, it still fails with following error.
No X11 DISPLAY variable was set, but this program performed an operation which requires it.
at LoadingGraphic.<init>(Unknown Source)
at LoadingGraphic.main(Unknown Source)