I'm pretty sure the rendering was visible. Or at least, I did not hide it in any way. The import wizard was visible on top of the main window.

I noticed that there is a short flickering of the image when closing the wizard. Maybe that could be related? I did not see such flickering on the previous Ubuntu version (21.x), but the rendering problem was in that Ubuntu version as well.

I noticed now that 6.6.2 at first does not show any renderings in the dialog windows.

I have recorded videos of the different Sweet Home 3D versions:
https://imgur.com/a/qY999R9