Symptoms

I turned off Energy Saver tool but the display stays dimmed.

Even Parallels Toolbox removal does not bring screen brightness back.

Cause

Under investigation

Resolution

Change Windows Power Plan settings to defaults.

Click on Start menu > Settings > System > Power & Sleep > on the right side of the menu click on Additional power settings to open up Power Options menu > here switch to Balanced (recommended) to revert brightness to the pre-Energy Saver condition.