Hi, after a lot of tinkering I've got it working on my Steam Deck. I'll tell you how.

First you need to install the Heroic Game Launcher from the Discover menu. Once installed log in your GOG account from there and just install the game.

Once installed, download the Verok's patch from this URL:
https://community.pcgamingwiki.com/files/file/2403-legacy-of-kain-blood-omen-veroks-gl-wrapper-patch/

Decompress this patch in your installation directory for blood omen (in my case it was /home/deck/Games/Heroic/Blood Omen). Be aware that there are a two items that you have to rename as they are in all caps, a folder named KAIN (change it to Kain) and a file named DDRAW.DLL (change it to ddraw.dll). You'll be prompted as if you want to rename your new files or overwritte the old ones, choose to overwrite.

Going back to the Heroic Launcher, if you go to "settings" for Blood Omen, the Wine version that worked for me was "Wine-Wine-GE-Proton7-20" (you may need to install protonup from the Discover menu to get it). Then click on "Wine CFG" and on the screen that shows up, select "Add new app" and browse for the "Kain.exe" on the installation directory. Make sure that Kain.exe is selected and go to the "Libraries" tab, and there add the library "ddraw" (a warning will pop up, just accept it). Edit that setting to "native then built in". With that, save and close the Wine window.

With all that done, try to launch the game from the Heroic Launcher. If it works, it should show a screen where you select the resolution and the language for the game along with some extras. Just click OK and everything should be working fine.

I hope this guide is helpful, as I had to go through a lot of research online for this to work.