I'm trying to figure out a way to enable DX12 for all the raytracing effects but it gives me no option to enable nor a different EXE. Anyone have an idea why?
Ok so I found out you need an extra executable from the GOG app (maybe available on the site) and launch it that way.

Edit your desktop shortcut so it looks like this:

"...\Ghostrunner\Ghostrunner\Binaries\Win64\Ghostrunner-Win64-Shipping.exe -dx12"

Alternatively there should also be a DX12 shortcut available in your start menu when you open "Ghostrunner [GOG.com]".

For Galaxy:
Press the Slider(s) button (next to the Play button) → Additional executables → Ghostrunner DX12

For someone who doesn't use Raytracing, what are other benefits of using DX12 for Ghostrunner?
So far it's only running less stable for me (game crash)...

Not that many. DX12 is great at decreasing draw calls and better multi core CPU utilization for pushing data to GPU.
Such functionalities are great for games with quilte a lot of moving parts (open world games).
Ghostrunner has quite static environments and limited number of enemies/dynamic elements.

Other then that, i don't recall any perf advantages in Shadow and Posteffects calculations, at least i didn't see much difference in that regard here.