Right, so if he isn't strong academically then it might be better anyway for him to do a smaller number of exam subjects than whatever school may have been pushing him to do in order to make themselves look good.
You might think about having a look at local colleges to see whether there are courses which might appeal to him for next year or the year after, and find out about about entry requirements. That might inform his decision about which IGCSEs to do and motivate him to work hard at them, if he thinks the entry requirements are achievable.
Another point is that if your son reduces his academic load, that would free up some of his time to spend on things which really interest him. That is likely to lift his self esteem. He has been spending all day five days a week working on academic subjects where the establishment has been giving him the message that his best isn't good enough. There is more to life than academics. Everyone says that, but you can see why a kid wouldn't believe it if his parents and his school nevertheless insist that he spends a vast amount of time and effort on academics and expect it to dominate his life.
If he loves sport or making music or creating websites or earning money, he could spend a significant chunk of his time doing those things instead. They might lead to a career one day. Or they might "only" lead to a happy, well rounded young person who knows his own mind and knows that he has talents which are valued by other people.
With home education there are no required subjects and there is no need to do formal sit-down academic work. My teen learned all subjects informally and did no exams, focusing on her interests of art, sports coaching, and music. At the same time she was doing various part-time and short-term jobs and voluntary work. She initially planned to go straight into work without doing any qualifications. She worked for a short while before changing her mind and returning to education, and is now doing a BTEC equivalent art course. She has just sat her English IGCSE at the age of 19, and will do the maths one next year.
To someone who measures the worth of an education by the number of qualifications achieved, the grades and the speed with which they are attained, this looks like a poor showing, a "Could Do Better" since she is of average ability. But this path is her own, and what she has learned will see her through all sorts of challenges in life. She's a well-adjusted, sensible young person. She's on track to go to university in a year's time if she wants to, and is undecided whether to do that.
Your son can make something of himself, even though he didn't do what his school wanted him to do.