As per the summary, when building debug and release builds from source, the documented cmake installation command only installs the release build.

I had to google the solution and found two old forum posts with the same problem and the same solution:

https://forum.qt.io/topic/139589/cmake-install-of-qt-build-does-not-install-debug-artifacts

https://forum.qt.io/topic/130545/debug-dlls-are-not-installed/3

Consider updating the docs here:

https://doc.qt.io/qt-6/windows-building.html

or where "-debug-and-release" is called out here:

https://doc.qt.io/qt-6/configure-options.html