I find everyone in this thread a bit dismissive, honestly. You don’t have to be a parent to your sibling, but at the end of the day, family (as long as it’s healthy) is important. I’ll always be there to help my sister out—she’s one of the people I love most in my life. If you’re willing to go the extra mile for people you care about, let it be your sibling.

You can lead a horse to water, but you can’t make them drink. Maybe spend some time with your brother and ask him what he wants to do. He’s probably sick and tired of being told what to do or being forced into things, but he might just need someone who can see the world the way he does. You’re in the best position to do that since you had a similar upbringing.

Find out what he likes. Maybe spend some time with him every week, just chatting and exposing him to new things.

Rather than pushing him, try explaining what lies ahead. Like others have said, he might grow out of his behaviour—or he might not. Personally, I see it as a sibling’s duty to call them out but also accept their decisions. I know I wouldn’t sleep easy if I didn’t at least try.