QML projects silently fail to load if they don't contain at least 1 ".UI.QML" file

This is effectively re-opening QDS-9460, since it seems to have regressed since the fix in QDS 4.0.1.

In QDS 4.1 LTS or 4.2, if the main "ui" filename doesn't contain ".ui.", opening/clicking the project does nothing the first time.  No user feedback or error message.
If you click on the project a second time, it goes to the Edit page.  Then you can click on the Design button, but only if you have the Mode Selector on (not default).
This issue can be reproduced by just renaming a standard new project "ui" file and its entry in the qmlproject file.
Note: Many QtQuick/QML examples in the normal Qt installation use the classic "main.qml" (or similar) and many contain UI elements.