You asked for it - we delivered! The per app toggle for Auto HDR on PC is officially available in the new Windows Insider Program build (dev channel)! Check it out!
From the store page:
Square Enix has temporarily removed this title from sale to work on some important updates. Please check back soon!
https://store.steampowered.com/app/224920/Legacy_of_Kain_Soul_Reaver/