@Mircea Please note that attaching pictures usually does not work in this forum. You need to upload them to somewhere and post links here.

You have to enable Use QML emulation layer that is built with the selected Qt in the settings, since Qt Creator does ship with Canvas3D.
Note that Canvas3D is not officially supported in the designer, though.

Glad to see you have you're problem fixed.

I managed to compile the needed plugin from source (Qt 5.7.0). It turns out we switched to gtk3. Copying the resulting libqgtk3.so into the qtcreator 4.0.2 release solves the issue.