create a shortcut to the 4.12.5 version of the engine and add the -D3D12 at the end of the executable full path
( in my case, in the the shortcut’s properties, the target is exactly
“J:\Epic
Games\UE_4.12\Engine\Binaries\Win64\UE4Editor.exe”
-D3D12
then launch the engine using this shortcut
and open your project using the engine project selection.
As I said before, UE4 project files can’t be opened directly, and that’s really annoying
Hope that will help you