Qt6 cmake configure error Unknown CMake command "add_qml_module".

Configuring 'qtquickcontrols2'
-- Using source syncqt found at: /qt5/qtbase/bin/syncqt.pl
-- Running syncqt for module: 'QtQuickTemplates2' 
-- Running syncqt for module: 'QtQuickControls2' 
-- Running syncqt for module: 'QtQuickControls2Impl' 
Configuring 'qtdoc'
Configuring 'qtgraphicaleffects'
CMake Error at qtgraphicaleffects/src/effects/CMakeLists.txt:7 (add_qml_module):
 Unknown CMake command "add_qml_module".

Debian 10

cmake --version
cmake version 3.19.1
CMake suite maintained and supported by Kitware (kitware.com/cmake).

em++ --version
emcc (Emscripten gcc/clang-like replacement) 1.39.8 (commit 372fb501244f29734b61f889a2ef24c2456a3484)
Copyright (C) 2014 the Emscripten authors (see AUTHORS.txt)
This is free and open source software under the MIT license.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

commit 3fc9dc5b8ef4c1c91d34fac820befa3b299ae01d (HEAD -> 6.0, origin/6.0)
Author: Qt Submodule Update Bot <qt_submodule_update_bot@qt-project.org>
Date: Tue Nov 24 16:54:11 2020 +0200

LANG=C ./configure -xplatform wasm-emscripten -nomake examples -prefix /usr/local/wasm -opensource -confirm-license