I think his failures and depression have as much to do with being viewed as “different” and struggling to fit in as normal.
I won’t try to downplay “rising to the occasion” but I think it may be more beneficial in the long run if the family (and the young man himself) focused more on doing/living what makes him happy, and focusing less on doing things a “normal” person his age should be doing.
Launching for him may not mean the same as it might mean for “normal” young adults in his situation. He might be happy with a different lifestyle, but may be uncomfortable expressing his desire for something different.
I have a friend who lives a very scaled back life as far as the normal college/career/marriage/kids/suburban home, but also very full. Both his parents have advanced degrees, his father was a professor and his mother spent a career in finance. He has an advanced degree, but lives in low-income neighborhoods, has never owned a car, works p/t at two different places as well as other occasional and/or contract employment and would be described as under-employed by many people. He’s a voracious reader. Is both a public facing person and is very happy being alone. His personality is … let’s say quirky, full, engaging, rewarding.
Now in his late 50s, he is very happy with his life. When he was younger, his family/friends always pushed him to “do more, be more, change” and that put him at odds with many of his loved ones. Once he dictated how he planned to live and what made him happiest, and they accepted that decision, he’s been as happy as a lark. Never married, though he’s had girlfriends here and there. No children. Not career focused or IRA driven or “goal oriented”. Simply enjoying the hell out of his life.
If the young man in your life is intelligent enough to graduate and self-aware enough to be high functioning, I think it’s time to allow him to choose his path. Some gentle guidance and mapping may be helpful. Some therapy from a counselor accustomed to working with neurodiverse people may be helpful. And open-ended understanding and acceptance from his family will definitely help. Let him be him, and relieve the pressure of hoping he “overcomes” his neurodiversity and becomes someone else.
Good luck!