affine example does not compile

Affine example does not build.

I compared it with other Open GL examples: "Scene Graph OpenGL under QML" and "Hello GLES2 Example" the both run.
I also double checked if I have all dependencies - seem to be fulfilled

sudo apt-get install build-essential libgl1-mesa-dev

tested on:
Description: Ubuntu 18.04.4 LTS
Release: 18.04
Codename: bionic

cmake version 3.10.2

g++ (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0

Qt from online installer.

{{Make Error at /home/anna/Qt/6.0.0/gcc_64/lib/cmake/Qt6Core/Qt6CoreMacros.cmake:440 (add_executable):
Target "affine" links to target "Qt::OpenGL" but the target was not found.
Perhaps a find_package() call is missing for an IMPORTED target, or an
ALIAS target is missing?
Call Stack (most recent call first):
CMakeLists.txt:22 (add_qt_gui_executable)

– Generating done
CMake Generate step failed. Build files cannot be regenerated correctly.
CMake process exited with exit code 1.
Elapsed time: 00:00.}}