I had the same issues. I’ve seen older issues related to this. I’ve tried all kinds of config changes, environment variables, forcing the composition pipeline… You name it. After all these years the situation with NVIDIA and KDE haven’t changed at all. KDE Plasma runs poorly on NVIDIA cards. Even a 10+ years old AMD card could run KDE Plasma way better than modern NVIDIA cards (including the new RTX models!).
KDE Plasma is my go-to desktop environment and I can’t see myself changing it in the future. So what options are left…?
I used to have a GTX 1080 Founders Edition in my desktop PC. I installed Manjaro KDE on it, and also on an old HP EliteBook which has an AMD 7570M mobile GPU. The difference between my two systems were day and night. My old HP EliteBook with that slow AMD 7570M could run KDE Plasma butterly smooth. I experienced all kinds of stutters and lags with NVIDIA on my Ryzen desktop PC (AMD 3700X CPU).
Finally I solved my problem. I ordered an AMD Radeon RX 480 8GB from eBay and replaced my GTX 1080 with it. All the lags and stutters are gone and I’m super happy with KDE Plasma (Manjaro). Everything became smooth and nice without any hacks. With AMD video cards every distro I tried works out of the box.
Since I simply don’t have the time to struggle with NVIDIA related problems nor I want to - this was the best option in my case. I will just ignore all NVIDIA products in the future, because it is simply a bad experience for me. This is sad, because I really loved my GTX 1080, but the product should serve the user, and not the other way around.