My OS is Kubuntu 20.04.
I got this ugly "grey area" on the top corner of window. No matter what theme I use, this "grey effect" remains there.
I've installed some themes from System settings > Global themes > Get new global themes
. But all the themes show this same problem.
Can anyone please help me out removing this?
Re. "No matter what theme I use", I don't see an ugly "grey area" with the Breeze, Breeze Dark, or Kubuntu Global Themes supplied with Kubuntu 20.04.
No ugly grey area with default themes
Your image indicates you're using themes obtained from elsewhere, perhaps the KDE Store. Please contact the developer(s) of those themes and ask that the issue be fixed.