I was wondering what the differences are for Ghostrunner specifically ? For me I noticed that the demo had more valleys than DX11 as it would have more drops into the 40's for frame rate while DX11 was a more constant 60+ experience or close to it. Visually I noticed no differences nor did I see any graphics options that were DX12 only.

Raytracing is DX12 only.
I think that's the only difference. Stick with DX11 until you want RTX.

And even then, raytracing seems poorly implemented and will destroy your performances/fps, even with DLSS. btw, I have a RTX 2070 SUPER at 1080p, yet, I get huge freezes.