If some private qt headers can not be found on your system, you have to compile qtwayland yourself and specify its location.
mkdir build
cd build
cmake -DCMAKE_INSTALL_PREFIX=/usr \
-DPRIVATE_QT_HEADER_DIR="path_to_qtwayland_builtdir/include/QtWaylandClient/5.11.2" ../
make
make install
Make sure Qt uses its wayland backend. If it doesn't, set the QT_QPA_PLATFORM environment variable to wayland or wayland-egl. To enable adwaita decorations set QT_WAYLAND_DECORATION to adwaita. If fonts appear to large set QT_WAYLAND_FORCE_DPI to 96 or 96 multiplied with your font scaling factor.
You can run the test application without installing it or the decorations directly from the build directory.
export QT_QPA_PLATFORM=wayland
export QT_WAYLAND_FORCE_DPI=96
build/bin/testapp