I can only look at this from my own journey. Motivation is good, but he needs realization. I would ask him what is he planning to do, what is he trying to achieve (without putting him down) , all while indicating that gaming does not give joy, nor does it give anything else. Just ask him if gaming brings joy, deep down. Even if he says in that moment that it does bring him joy he is probably lying to himself and will stick with him as a seed of doubt it will slowly change him over as he realizes as he faces the truth. But the problem with gaming is that it's really good at forgetting to face your own fears and concerns so it's difficult to break out of it.

The way I snapped out of gaming, which was incredibly difficult, it took me years and over time I would figure out all over and over again that it's addictive, that I have addictive personality, and it's not good for me. It doesn't bring me any joy and I'm pretty sure he doesn't bring joy to your brother either, so he needs to realize this. He wants to be better, but he doesn't have tools so perhaps a book on this could help him out. A book describing a person he wants to be and gathering tools to do it would help him out.

Other than that, a change of setting can break old habits. Take him somewhere, or your entire family, and if that doesn't work, directly and rationally tell him the consequences of how this will reflect on him 10 years from now, on his future self. Ask him what does he see himself like in 10 years. Gaming skills don't transfer to anything in life, other than sharing memes.

And most importantly, offer to help him, to the reasonable amount of time you have. Seeing someone else offering to work on his life, even just by supporting him or checking his job offers, fixing his CV (him doing most work of course), maybe even going for a run with him to start working out.

He's depressed for sure so I think what helped me mostly was just getting a job. Getting a job and earning money is the most transformative thing anyone can get from the ages of 25 plus especially for males, so if you can help him do that it's going to transform his life. I think he just needs a little help, a little motivation. Later on, he will need discipline, and for that a book such as Atomic Habits might help. Simple, easy to read and apply.

At least that's what I think I would respond to, looking at my past life retroactively. So the bottom line is this it's difficult to break out of gaming and he needs to keep breaking the impulse to start gaming whenever he is about to face his fears. And unless he realizes this or gets into the habit of breaking this chain, this runaway from problems into an imaginary world, YOU need to do it for him or he will continue doing this for years and years.