Since you are using Nvidia, you receive no benefit to using D12 no matter how powerful your system.
https://us.forums.blizzard.com/en/wo...ications/15418

With the Battle for Azeroth Pre-Patch, we added support for DirectX 12, solely to improve performance on certain hardware. NVIDIA’s DirectX 11 support is already heavily optimized for WoW, to the point that there is currently no performance increase to be gained through our current implementation of DirectX 12 for WoW on NVIDIA systems.