Quick one: Set the proper CMAKE_PREFIX_PATH value for Qt5 development on Windows 10 with MinGW and CMake.

Here is the lovely error you get from CMake.

CMake Error at CMakeLists.txt:13 (find_package):
 By not providing "FindQt5.cmake" in CMAKE_MODULE_PATH this project 
has
 asked CMake to find a package configuration file provided by "Qt5", 
but
 CMake did not find one.

 Could not find a package configuration file provided by "Qt5" with 
any of
 the following names:

 Qt5Config.cmake
 qt5-config.cmake

 Add the installation prefix of "Qt5" to CMAKE_PREFIX_PATH or set 
"Qt5_DIR"
 to a directory containing one of the above files. If "Qt5" provides a
 separate development package or SDK, be sure it has been installed.

CMake asks you to tell it where to find the Qt5 *.cmake configuration files. One option is to set the CMAKE_PREFIX_PATH variable. The Qt5 documentation has the following to say about that:

The easiest way to use CMake is to set the CMAKE_PREFIX_PATH environment variable to the install prefix of Qt 5.

Now, what the hell is the "install prefix"? It turns out it is the path where you can find the compiler-specific Qt binaries, include files and the other stuff. In my case, using MinGW, it is located at "C:\Apps\Qt\5.14.2\mingw73_64". If you are using the MSVC binaries, select the corresponding directory, probably something like "C:\Apps\Qt\5.14.2\msvc_2017".