It's not much more than a "Me too" but I wanted to add that I have this same issue on a fully updated Windows 10 installation.
Windows 10 Pro 1809 (Build 17763.134)
Nvidia RTX 2080 with latest drivers (as of 12/4/2018) 417.22
DX12 option does not appear in menus. I also attempted manually enabling it in the profile and deleating the /twinkle folder to redownload it.
Getting to use DX12 (and RTX) would be real cool, ahaha.
Any update on this!.. I had the DirectX 12 running and one day the option no longer shows in my menu. i really dont feel like re-installing windows!!
