Viber + KDE + Wayland + Nvidia = fully transparent

I have tried out again the Wayland on my testing Manjaro + KDE Plasma + Nvidia 1050Ti system. It is a pleasant surprise for me that a lot of things work properly, most softwares run normally and I only had to adjust a few ones (e.g. GPXSee, Birdtray) manually. The only software that gives me a headache is the Viber. It starts with fully a transparent window, only the window borders are visible. It looks as it works, because the mouse pointer changes its shape according to the (invisible) content of the window. On my system the QT_QPA_PLATFORM=xcb viber does not help.
Is there any other trick that can help to run the Viber?
I wonder if the Viber runs on KDE Plasma + Wayland + AMD or not?

What about flatpak version?

The same transparent window appears with the flatpak version, as well.