Massive increase in FPS in Xplane 11 using Vulkan. Also Aerofly FS2 is so very much faster too. DX12 should more or less be equivalent, depending on how ASOBO program it.
Good explanation is here, courtesy of MicroSoft:
https://docs.microsoft.com/en-us/windows/win32/direct3d12/what-is-directx-12-