Here's a Small Trick That May Improve the FPS in Black Desert Online
- go to your Black Desert Online installation folder, and find the Black Desert launcher;
- right click on the file and choose Properties;
- from the Compatibility tab, check the "Override high DPI scalling behavior" box and then hit OK;
- restart the game and check whether your FPS improved
This can also be applied to the Steam version. Tell us if that works if you try it.
Source: mmoexaminer & reddit