Oh, this is such a specific niche and I love it! It's a really fun intersection of dark fantasy, supernatural elements, and LitRPG/progression structures. While the exact phrase 'devil gamer' isn't super common, the concept of a demonic or infernal character who is also deeply embedded in game mechanics or uses gaming-like powers pops up in a few places. Rebecca Zanetti's 'Dark Protectors' series has warlords and vampires with magical abilities that sometimes get described in almost tactical, game-like terms, though it's not explicitly a 'gamer' setup. More directly, you might look at some translated webnovels on platforms like Webnovel or Royal Road—titles like 'The Devil's Cage' often feature protagonists who are literally devils or gain infernal powers within a game-like system or an isekai framework.
I feel like the closest match in trad-pub might be in the darker corners of urban fantasy where the magic system is very rule-based. Think like the 'Dresden Files' by Jim Butcher, but if Harry Dresden was less of a wizard and more of a hell-bound entity crunching numbers on his spells. Honestly, most of what I've stumbled across with this exact vibe is indie or online serials. It's a trope that thrives in spaces where gamelit and paranormal romance or dark fantasy collide. The character archetype is usually about leveraging infernal contracts or demonic energy through a lens that feels suspiciously like min-maxing a character build.