I know this probably isn’t of use right now. But I used to love gaming and computers. I have made a career out of it and went to university for coding and programming. While I understand the want to try and persuade him to try other things, which is the right thing to do, don’t feel too much pressure for his passion for gaming etc
I’ve seen and heard a lot about dopamine addiction through screens especially in children (not saying that he has an issue with that I do not know) but screens are tricky to deal with because of that. Maybe looking into solutions they have found that could help you find ways to help him find interest in other activities? Sorry not a solution but a place u hopefully could find one!
Graphic design means drawing. Can he be drawing on his tablet? Maybe offer to stretch the rules that he gets an extra 1-2hrs on the screen if he spends that time doing a Graphic Design project. What other skills does a graphic designer need that he could be working on? Might be worth researching what off-screen skills are needed (probably includes people skills/presenting/working to a brief/market research!) Can you enrol him in a sport? Lots of councils offer youth sport tasters during Easter/Summer holidays, maybe have him try self-defence/team sport, if there's anything he doesn't hate, sign him up 😂 Nerd Fitness (website/online community could provide some inspiration for how to talk about this, they align different sports with game/film characters to reframe exercise. Are you training to be a barbarian or an assassin? Can you get Dad on board with what you're trying to achieve? Do you have any local gaming groups or hubs where he can meet and play with other gamers in real life?