Overview
This is how to enable ultrawide support for the game
Instructions
Download the latest version of niohresolution.exe from here: [link]
Place that file in the nioh.exe folder, located in ~SteamsteamappscommonNioh
Run the niohresolution.exe
Launch the game, and in the launcher settings, change quality to high and resolution to 1920×1080 and save the settings
Now when you click on launch game it the UltraWide fix should be enabled.
I did not create this, all credit goes to [link] and jackfuste from wsgf forums.