At 24, he needs to be motivated to improve for any improvements to be possible. You can’t force it. It’s no longer under your control. But you can stop enabling him. How is he paying for drugs and alcohol without a job? Why is he allowed to live in your house and show such disrespect?
It’s true, assuming he has ADHD, that life is more challenging. However, that doesn’t mean it isn’t possible or that he should get a free pass. Available treatments are very effective when you work them. Cut him off (at least financially, even if you let him stay in the house) until he’s shown over a several month period that he’s working on treatment and self improvement. Holding his hand is only encouraging him to do nothing.
Or, accept that this is your reality now. He has no reason to change.
I was him until the last family member booted me out. It’s the most loving thing they ever did. Yeah, I hated them at the time, but once I got on my feet I realized it was just what I needed.