

Another vote for scratch. Most kids that age want quick results and not to spend ages debugging something. Funnily enough I’ve seen the same scratch interface used to program industrial robots.
How much time one on one are you committing to spend with the child? This will make the difference.
Alternatively, think about some sort of robotics kit. Doing stuff in software is great but if it changes something in the real world, even better. Have you thought about something arduino?
Just for balance though, make a raft, a treehouse, a tent, make a fire without matches. It’s all problem solving but I bet any kid will remember getting muddy more than writing a neat while loop.
Have you talked to the school? They may be able to help out, particularly if he’s already in the queue for a diagnosis. Maybe a note from your doctor would support this.
Help may be tuition support, guidance or even some extra time in the exam room - or doing the exam in a different area.
Anything you can do to stack the odds in your favor can help, and the worst they can day is ‘no’, so there’s nothing really to lose.
Finally, though exams are important, they are not the end of the world. They can be retaken later if necessary so try and remember to keep things in perspective and manage the stress accordingly.
Finally finally, good luck to you and your son.