I feel sorry for him. Clearly he is one of those pupils who struggles with self motivation. That's not necessarily laziness. He could just be the personality type to thrive in a busy classroom and has got utterly lost along the way.
I'd be really kind, not at all angry and say gently that he's a bit young to decide school doesn't matter because it will impact on the rest of his life. Ask him what the hardest part of remote learning is, what he hates most about it. Then ask him what he thinks helped him get into top sets when he was at school - what motivated him then. Ask him to help you work out some ways to replicate that atmosphere of learning. Also tell him that it's worth apologising and asking for a second chance and really pulling out the stops to get his work back on track.
Go through every subject with him and make a snagging list of every single piece of work he's not done. Help him organise his files and books and materials. Focus on the core subjects - Maths, Sciences, English and a couple of his other favourite subjects. Agree to let one or two subjects fall by the wayside for now - as long as they are not core.
Set him up to do a piece of work. Check he has all materials he needs, give him a timer and tell him to do his best. If there are pieces of work he doesn;t understand, put them aside and focus on ones he can do relatively easily. Use brilliant Khan Academy to explain maths issues.
Get him to submit the work with a grovelling apology saying he lost his way and he really doesn't want to drop down two sets. Get him to make a good case for staying in top set for his favourite subjects and core subjects if possible and maybe accept he might be in set 2 or 3 for some of the others.
I say all this because DS struggled massively at that time and we thought of moving him as he was at a selective school. But it turns out he had ADD and just hadn't a clue how to organise himself - not his stuff, his thinking, his planning, his approach to tackling an issue. Each stage needed to be very careful designed for him and he had to be taught how to tackle things one by one. But he learned. And now he is the most organised student, getting firsts at uni with an immaculately tidy bedroom. He just couldn't work it out for himself without masses of initial support.