Ok. The whole college process and student funding is quite different from, and often more complicated than, many other countries.
i know there are some articles on student funding on nerdwallet - it’s generally a good website but I haven’t read those specific articles, but they might help make it a bit clearer for you. For anything funding or admission related, when websites might say “domestic” or maybe even just “us citizen”, those always include green card holders.
(Well...the military academies may have a usc restriction, not sure. actually if your son has any interest in the military then ROTC is something to look into as well,
https://www.todaysmilitary.com/education-training/rotc-programs, they help pay for college and then in return you serve for a while. And while we are on that tangent, make sure he registers for selective service as required of green card holders when he turns 18, he could have problems naturalizing if he doesn’t.)
is your son a senior already or are you looking ahead to applications later this year?