so i have an Optimus Laptop with Intel and Nvidia GPUs, every think works fine on the Intel GPU but when i switch to Nvidia all Desktop effects stop working and also the blue effect of the Kvantum theme.

Nvidia Graphics Driver Version: 440.59
Kernal Version: 5.3.0-53-generic
Distro: KDE Neon 20.x

so any thoughts about how to fix it?

Hi! try alt+shift+f12 that's the shortcut to enable desktop effects