You wouldn’t know it from the description, but Compound Fracture, a mod for the original DOOM II videogame is claimed to be…

my 10-map episode based on Nyarlathotep and Yog-Sothoth. The final boss is supposed to be Yog-Sothoth.

I learned this from finding a new forum thread, which jogged my memory about the game. Greatly enjoyed by me at the time, along with the fantasy variant Hexen. The forum thread also suggested the mod Rylayeh for DOOM II.

Via search, I found five more mods (aka wads) that are substantial and have good reviews…

Shrine 1.2 for DOOM II. A “Lovecraftian Total Conversion mod!”

Void for DOOM II. “Lovecraft meets Lewis Carroll”. Uses ZDoom.

Strange Aeons v5.7 for DOOM II. Huge Lovecraftian total conversion. Uses ZDoom.

Beyond Kadath for DOOM II. “A story-driven WAD roughly in the vein of H.P. Lovecraft’s Cthulhu Mythos.”

Maskim Xul for DOOM II. “One of the winners of the 2018 Cacowards.”

The game itself can be had on CD via eBay for around £15. It’s obviously become collectable, despite the vast quantities it sold, and the days of getting a jewel-case for £1.99 inc. shipping seem over. More affordable is the download at GOG.com for £4 including “the enhanced re-release” of 2019. Then you download ZDoom / GZDoom and run it through that, giving the old game enhanced powers. You may also need a Flashlight++ mod.