I think the best thing is to take him to the library or to an independent bookstore and see what catches his eye. Even better if he can spend some time talking to the librarian or bookstore employee to hear their suggestions.
Another idea is to google "[state name] reading list" or "award list". usually each state has an award list made up of books from the last 2-3 years, broken down by age range.
Here's this year's list of nominees for the Maryland Black Eyed Susan Award:
https://www.maslmd.org/current-nominees