Have him think about bigger things

 

Don't do everythig for him, let him do for himself in his own way, and then praise him for his courage and resourcefulness.

Ask about his opinion on things/events, no right or wrong.

Find a place (hours away by car, some historical site) he wants to see.  Give him a paper map (no GPS on the road, but he can look it up on Google map before the trip to plan), and while you drive, let him sit next to you and direct. Give him the title of "navigater."  If he makes a mistake, don't blame, let him correct it, you just drive.

Larry Gonick's "Cartoon..." books.  Ask him about what he read and provide more if he finds interest in a subject or topic, suh as ancient Rome, WWII, etc..

Enlist the help of big sister.  She shouldn't belittle him, but help him find his meaning in life.

Go fishing.

 

(Now, he lacks agency, a word with one of of its meanings lesser known, or to say: he needs to believe in his own agency.)