Using qt_add_plugin outside an internal Qt build errors out

25/10/2020 the problem still exists in Beta1
Make Error at /home/anna/Qt/6.0.0/gcc_64/lib/cmake/Qt6Core/Qt6CoreMacros.cmake:1285 (qt_internal_add_plugin):
Unknown CMake command "qt_internal_add_plugin".
Call Stack (most recent call first):
plugin/CMakeLists.txt:22 (qt_add_plugin)

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.

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When using qt_add_plugin in a cmake project outside of Qt it will error out with the following:

CMake Error at D:/path/to/qtbase/lib/cmake/Qt6Core/Qt6CoreMacros.cmake:1280 (qt_internal_add_plugin):  Unknown CMake command "qt_internal_add_plugin".
Call Stack (most recent call first):  src/CMakeLists.txt:9 (qt_add_plugin)

Following the logic of the if-statement at that location it can be worked around by either calling qt6_add_plugin directly or by setting 
"QT_DISABLE_QT_ADD_PLUGIN_COMPATIBILITY" to TRUE.