okay that’s so great !
I tested changing QT_QPA_PLATFORM=wayland to QT_QPA_PLATFORM=xcb in /etc/profile.d/librem5-wayland.sh
now I have the same behavior in all cases because it uses XWayland all the time
I understand the change I made is not a good long term tweak
The QT_QPA_PLATFORM=xcb should be set case by case in the launcher or alias of the app you want working with XWayland
For those who could be interested, here an exemple for qtqr :
You need to edit the file /usr/share/applications/qtqr.desktop and modify the line
Exec=qtqr %F
to
Exec=env QT_QPA_PLATFORM=xcb qtqr %F