>I have a Samsung disk SSD. https://ssd.userbenchmark.com/SpeedTest/396/SAMSUNG-MZNTD256HAGL-00000
>I also have a VHD for my main data on drive d:.
>Something appears to make things go slower as months go by. I am still trying to find the reason.

I have observed that Windows itself slows down exponentially the more software you have installed. I think it uses a slow top-down directory-like scan/search for accessing registry entries, resulting in increasingly slowing down over time.

Try running one of those registry cleaner optimizers and see if that makes a difference. I've observed some notable speedups at various times in Windows when I run those, especially if I have installed software and later uninstalled it.