If he’s consuming right wing social media, it might be because he’s bored. Others have suggested left wing media, but maybe just finding other activities to do would help. These cost money, but maybe camping/hiking, hobby electronics/combat robots, dirt bikes/go-karts, RC planes/drones or metal fabrication are ideas that come to my mind. These are hobbies that have either politics neutral or left leaning communities. If he picks up that you’re trying to politically influence him, he’ll likely dig his heal in.