21 y/o family member, with some disabilities, where to start

Hi, I have a nephew who is now 21. He was always on medicaid as a child, when he was 19 or 20 they kicked him off, his parents did not have him insured. As a child he received mental health help, took medications etc. He has been living with me, and I want to help him, where do we start? His parents are not an option and my nephew does not wish to have communication with them at this time.

We applied for medicaid (denied) based solely on his income (he is able to work part-time at walmart pushing carts right now) He was enrolled in college, but right now we do not have the funds to re-enroll.

His diagnoses (we are still waiting for copy of medical records) Autism, ADHD and underdeveloped prefrontal cortex. He has experienced alot of Trauma as well, but this only came to light recently.

I'm most concerned with getting him to a regular therapist for his trauma. Likely returning to some of the medications he took throughout childhood as well for ADHD specifically.

Specific questions:
He was denied medicaid, would reapplying with his diasbility information help with that? I didn't help him fully with the application, but he said they didn't ask.

Is medicaid not even the right thing we should be applying for?

I also think once he has medical assistance he will be able to work more, if that makes sense (therapy and medication) is there a way to help medicaid understand that?

Obviously not sure what I should be doing, but I want to help him, any advice is greatly appreciated. Live in Nebraska if its relevant.

Thank you

Forgot to add, looking for a way to add him to my employer insurance as well, but haven't had luck figuring that out either. As he is not my bio child and not adopted (again he's 21).