And if you run in borderless or windowed it works fine, is that right? If so that is the exact opposite of the normal experience.
DXDIAG is a program you run from the Windows search box on the task bar. After running it will open a window and start collecting info with a progress bar in the lower-left corner. When it completes click the 'save all information' button and save it to a file then attach that file here.
Please attach here your Documents/Paradox Interactive/EU4/settings.txt and pdx_settings.txt .
From your Documents/Paradox Interactive/EU4/logs/ folder, attach here system.log , error.log .