Maximize windows by dragging them to the top of the screen and alt+tab freezing entire system for 3-5 seconds. I mostly tried everything that i can find with some search. I'm using nvidia-430 driver. In nouveau driver there is no problem like that or when i play some games (those are disabling desktop effects). I think its related to nvidia driver. So please enlightenment me guys.

My gpu is gtx970m.
Kubuntu 19.04.
Kde plasma 5.15.5

I have same issue. Does your laptop have Optimus? I have an Optimus laptop with a Nvidia quadro card and internal intel GPU. When I enable the Nvidia card I have found that im getting freezing when window snapping. I just saw this bug https://bugs.kde.org/show_bug.cgi?id=406180

I do also have the same bug when using OpenGL compositor, had to drop it off and switch to XRender.