Well the DX12 in the sim is still in beta.
DX12 is also a lot more unstable - Recently played Dying Light 2 and am currently playing the updated Witcher 3. Both more unstable with DX 12. Don’t know if it’s the Ray Tracing or DX12 itself but HUGE numbers of crashes. Even Civ 5 still crashes when using DX12 and that game is ancient