For those who doesn't know base unmodified Unreal
Create a Shortcut add [] whats in those
in the Root
Kalyskah_RPG.exe [-dx11]
or
\Kalyskah_RPG\Binaries\Win64
Kalyskah_RPG-Win64-Shipping.exe [-dx11]
The Game itself has not yet the complexity that would really require DX12 anyways with good optimized Drivers and you wouldn't yet lose so much users at all but forcing them on DX12 i guess you lose much more potential customers for now
Just be sane with the Post Processing overhead and everything will be fine, or optimize it apart from Epics current default
DX12 in it's current state for this title could help in Unreal Streaming related issues here give you a smoother experience on Windows 10 in that case, but its for now case to case config base specific if you gonna see real experience able improvements or not if things become real complex and the per core overhead extreme then surely everyone will gonna experience the boostups, especially in those high latency dropout situations with heavy usage of blueprints if you not going fully native.
I also do not really see that it was heavily optimized for a HDR usecase (proper calibration especially) so you not really gonna lose anything perceptional here really either.
And implementation of DXR is also not ontopic here.
So let the API Benchmarking for Kalyskahs case begin