Just outright ask him what he's interested in. That we have time now to explore something new, that you can help guide him and maybe lay out a little cash to help him pursue his interest. Then give him some time to think about. Tell him to see you when he's ready to discuss it.
You might be surprised at his answer. Heck - even if it is a game, many games can teach skills. Negotiating, math, reading, memory, coordination, persistence, possibly even develop an interest in programming. I have a physicist son who memorized the original 151 pokemon, in order, without looking at a poster or anything, at age 8 or so. Obsessions aren't necessarily a bad thing. And if you learn a little about his interest you can have something to talk about, and eventually he might talk to you about something personal again.
Having everybody eat at the table together as a family helps too. I always found when I asked about my kids interests at bedtime, or asked about homework at bedtime they would talk just so they could stay up later. And I pretended not to notice the time. But your boy is 14, the last few suggestions might not work now.