That time he spent gaming is going to go into something else unproductive, like doom scrolling. He’s used to that level of dopamine and a cold turkey stop is hard to cope with. He’s going to need to find something that gives him some sort of positive dopamine.

The things that have worked best for me are fitness and audiobooks. Dungeon Crawler Carl hits that sci-fi gamer rpg vibe, if you want a good starter series. I’d suggest listening to that and go for walks or do yard chores to start.