Hi,
Thanks for the update, May I ask, Which GPU or graphics driver do you have-Intel, NVIDIA, or AMD-as integrated Intel graphics can sometimes cause this even on systems with another GPU? Do you have any monitor management software installed, like Dell Display Manager, HP Display Assistant, or LG OnScreen Control, that might add window overlays? And does the white box appear on all monitors or just your main one, and only when dragging windows or even at other times?
Regards,