I know that the "David adopts max at the end of the summer" scenario kinda died but I dunno man.
imagine max just choosing to spend time with David. choosing to help out at the summer camp. choosing to start spending time helping out outside of camp activities. (finding him online and messaging him stuff. getting his first phone and adding David to his contacts because he has it memorized)
I'm kind of obsessed with the found family idea being less forced upon Max and more of something he chooses. even if David doesn't legally adopt him, David still gets father's day cards and other cheesy stuff.