My DS is 14 and has some SEN and also has epilepsy. Currently, the epilepsy is more problematic in extracurriculars as he's increasing in social confidence, though he doesn't do much in the way of really challenging extracurriculars e.g. competitive sport/high level instruments. One of his needs is dyspraxia but he's very up for having a go at a lot of things that he will never be a professional at.
It's probably time to ask if he wants to do DofE (anything with a badge is usually a yes for him). His school doesn't run it but he can do it through Scouts.
We can find a skill and a physical activity for him as he does guitar, some skill type activities at home, or at school but he could take them up independently, and he goes to junior Lifesaving and disability skiing.
It may be a difficult task to find an expedition that will take him (currently Scouts ask us to go on camps, though not to sleep in with him - partly for safeguarding but also thankfully he hasn't had a fit in his sleep for years) but we can make some enquiries.
I'm just wondering what your DC have done for volunteering. Not all the ideas will suit him - and some won't be available to him (e.g. his school would not let him listen to younger children read, and I doubt the nearest primary school to his school would let him either) or that interesting to him, but I thought it was worth asking for All The Ideas. So just dump them here, don't worry if I've already mentioned them or if you aren't sure if they'd work for him.
So far I've thought of helping at Beavers, even if it's mainly doing the drinks and snacks; volunteer maintenance at one of the local Scout camp sites; and volunteering at one of the local parks (there are two that have regular volunteering mornings, but one of them is during the school day, and they are each only once a month so that might not work).