Right click on eu4.exe , properties, compatibility. Tick "disable fullScreen optimisations" untick every other box in that dialog, Apply and exit.
Edit settings.txt to say:
refreshRate=60
fullScreen=yes
borderless=no
vsync=no
Then in the launcher Game Settings menu, select fullScreen display mode.
IF that doesn't help:
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/Europa Universalis IV/settings.txt and pdx_settings.txt .
From your Documents/Paradox Interactive/Europa Universalis IV/logs/ folder, attach here system.log , error.log , exceptions.log .