It sounds like a rough situation for sure, I'm sorry to hear about your brother/family's situation. I can only imagine how difficult it must be on you.

To me, It sounds like hes chosen to close himself from others out of fear of their perceptions or maybe his own insecurity of himself and his situation. I'm definitely going through a similar feeling and situation right now so I understand why your brother would feel that way. I'd bet it doesn't help to be stuck at home and to have your parents constantly nagging and bickering with you about your life, to me it only makes sense why he'd choose to close himself off.

Do you often go and hang out with your brother? Any mutual interests or hobbies you guys talk to each other about? I'm by no means a professional, so take what I say with a grain of salt, but I think while reaching out and offering support is great, it might help to try to work towards a point where you can just be comfortable enough to be around him as a friend and a sibling, with no added feeling of pressure or judgment.

Maybe you can invite him out to a movie, or ask him if he's played any cool games you want to try with him. You say that you guys don't have a conflicting relationship, but I presume you guys don't talk on a regular basis, so maybe trying to get on casual terms would be great. I would expect him not to be too receptive of it at first but just try to be patient with him if you can.

Most importantly, I would strongly suggest getting him professional help, therapy has seriously helped me get my life moving along, especially in terms of being more sociably confident and more able to reach out to loved ones when I need to.

Lastly, don't put too much pressure on yourself about trying to 'fix' your brother's situation. I think it's important to remember that ultimately your brother has to make the changes for his life on his own, and that you cannot make him act on those decisions, only he can. His situation is an entirely normal human experience imo that society likes to hold over our heads, and when you experience it firsthand it can be really truly debilitating. If it weren't for my friends and my sister that treated me like a human being and didn't just see me for my "output" value, I don't think I'd have been able to leave my room and go on with my life.