Describe the bug
Backing store is not working on Qt6 using QOpenGLWidget

To Reproduce
to build run the following command:
qmake-qt6.sh -spec linux-g++-64 ; make clean all

run the following command
./LDView -platform wayland ../m6459.ldr

Expected behavior
Clear background is expected

Screenshots

Platform (please complete the following information):

• Linux
• Qt 6.x

Additional context
Same issue ont Qt5 if option QOPENGLWIDGET is enabled.
Without option QOPENGLWIDGET blank window is displayed on Wayland.