HDR (and for me - Fullscreen-Mode in general) is broken on NVIDIA GPUs and just makes the screen change modes to HDR and back until you kill the game or force it into Window-Mode by hitting ALT+ENTER at the right time.

A user named NanoHDR has kindly provided a patched game executable (Nino2.exe) which fixes this issue, since the developers seem to have no interest in this.

Since the patch only requires a single byte to be changed in the executable, i thought having a method of doing this yourself is a good alternative if the Google Drive link ever gets taken down or you feel uncomfortable launching unknown files.

1. Start PowerShell, you'll get a window like this:
   
   
   
   
   
   
2. To ensure the shell is pointing to your user directory type
   
   cd $home
   
   
3. Copy the Ni No Kuni 2 executable (Nino2.exe) from your game directory
   
   [Steam Directory]\steamapps\common\Ni no Kuni II Revenant Kingdom
   to your user directory
   
   C:\Users\yourName
   
   
4. Type (or copy) the following into powershell (this reads the whole file, replaces the required byte then writes all of it back)
   
   $wFile = (Get-Item .).FullName + "\Nino2.exe"; $bytes = [System.IO.File]::ReadAllBytes($wFile); $offset = 4624974; $bytes[$offset] = 0xEB; [System.IO.File]::Move($wFile, $wFile + ".bak"); [System.IO.File]::WriteAllBytes($wFile, $bytes)
   
   
   
   
5. If everything worked you should now have a Nino2.exe and a Nino2.exe.bak in your user directory, Nino2.exe is the patched file, Nino2.exe.bak is a backup of the old one.
   
   
   
   Copy these files back to the game directory (overwrite existing files) and you're done.

If anyone is interested in the exact byte that is changed:

0x74 at Offset 46924E is changed to 0xEB