Make the characters' lives outside the game intertwine with the ones they have in-game. The "stuck in-game" meta died out, with SAO, despite them still milking their fanbase several years later. Nowadays, the only primary way of making gamer stories is through system stories or transmigration with level-skill trees. I don't know if you're going either route, but that's all you got to intrigue new readers.
However, with the world constantly in conflict, people want to start escaping from their everyday lives and become enveloped in relationships between friends, family, and the like. I suggest that you find a way to add Slice of Life elements to draw in potential fans from another niche category. For my story, High Royals Gamer Club, I created a club of high schoolers who all love to game, though with different personalities and on various systems. The main character is inept in video games and is forced into the club by her boyfriend Along with that, she's moody and stuck-up (room for character development), doesn't like taking advice (chances for relationship improvement), and spoilers that her boyfriend, who forced her into the club plays the same game along with her close friend-group, either side doesn't know that they play, so things get pretty tense and interesting towards the end.
I don't know how your book will be plotted out, but if your character is going to be OP make them have some sort of struggle to be relatable, whether with life choices or internal problems. Think Saitama from OPM or Mob from Mob Psycho.
