The key is to make the learning stick is apply it to something he is motivated by. Help him find those points where he begins to lose focus. That’s when he needs to go outside and just yell at a squirrel. The squirrels won’t take it personal and it helps throw the switch to reset.
I work with college kids every day with ADHD, autism, the whole list as a student success advisor. The big challenge is not to let your son get down on himself. Kids tend to become their own worst enemies when they can’t meet their own expectations. At some point they will start saddling up to depression and when they climb in that hole it is tough to crawl out. There is a reason I am the only non-engineer in my family and proud to be a PE major.
Have him make appointments with himself in his phone. I will make appointments with my self for when I have a report to do. That helps me begin to focus on that task. No quick fixes. Some of it you just have to grow into with experience to reference what works / doesn’t work for the individual. I have my doctorate and it took a while to get to and through it. If I can do it anyone can.