That white pixelation on apps with a dark theme is not caused by a Windows system problem, it is almost always caused by the graphics drivers.
The best option is to completely remove the current graphics driver using the widely available free DDU utility, then restart your PC and go to the support page for your PC on the manufacturer's website to download and install their recommended version of the graphics driver.
If that does not resolve the problem, go to the graphics card manufacturers website to download and install a couple of versions of the graphics drivers they provide to find a version of the drivers that resolves the pixelation.