Some other things to consider beyond drugs:
If possible, see if you can find something to occupy his mind. If employment isn’t a possibility, then hobbies or volunteer work. Employment is commonly cited as a helpful by highly functioning people with SZ.
I think there’s some truth to the initial name for schizophrenia being “dementia praecox” or early dementia. There’s similar gradual deterioration of brain mass as in dementia, and similarly there’s a case for “use it or lose it” where this is concerned.
So I’d consider encouraging what we tell our elders to do to keep their brains more healthy. Work puzzles, exercise, learn new things, enroll in classes, finish college, actively participate in the world, engage with music and art etc.
I’m a bit of a rare case, but my whole professional career was after my diagnosis. Yet I kept busy. I took pottery classes, I learned to sing and act and kept myself engaged in the world-- and although I haven’t had any brain scans, I speculate that the mental stimulation had benefits by building neural connections-- perhaps routing around some brain deterioration from my first year of walking around unmedicated.
It sounds like he may be engaged in social media which is a start, but I’d strongly encourage engaging him IRL instead. My opinion is that many people with SZ live in impoverished mental environments which only furthers the brain deterioration. While it may be easier to sit at home and smoke, eat and watch TV or engage with computers or video games, I think there’s more benefit engaging with the world. He’ll probably suffer from avolition and other negative symptoms and the outside world may overstimulate him, but from my experience learning to live in the real world has tangible benefits for recovery.