From the Steam Community page....worked for me
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Originally posted by Malfury:
My Fix
1. Turn off Steam.
2. Navigate to C:\Steam\steamapps\common\Bless Online\Engine\Config
3. Open BaseSystemSettings
4. Search for "ResX" and "ResY"
5. Change it to your NATIVE RESOLUTION. (ex. If your monitor is 3840x2160, ResX=3840 ResY=2160.)
6. Navigate to C:\Steam\steamapps\common\Bless Online\Launcher
7. Open the BlessLauncher and DO NOT TOUCH ANY OTHER SETTINGS.
8. Press the red shiny button and enjoy.