It’s awful when they won’t settle, and for most of his life he’s been confined to home so the usual activities that would help him develop haven’t happened. He sounds really overwhelmed being away from you, I wonder if strategies we use with adopted children might help you?
Things like having a transitional object (a cuddle toy, comforter or the like) that you sleep with, so it smells like you to take to nursery. Or giving him something to look after for you until you come and pick him up, or you having something that you look after for him. What you’re aiming for is for him to know that when you leave, you come back again - and that you continue to exist when you’re away from him. Where attachments are insecure (ie children can’t bear to be away from you) it’s sometimes because they don’t have a sense of permanence ie that when you’re not physically with them, you stop existing in their mind.
My DS was a bit older than yours but he’d give me a cuddle toy if I went away for work. I’d send him photos of me and the cuddle toy doing things together etc.
I’d also talk a lot about how much I’d miss him, be thinking about him, what I’d be doing while he was at nursery, what he’d be doing at nursery etc. When I picked him up I’d be chatting about how much I missed him, what I’d been doing, what he was doing. I’d also start the day talking about what we’d do once nursery was finished, to reinforce the idea that I was coming back and that we’d be doing things together.
Also worth playing Theraplay type games with him (if you google there are loads of resources). They are very simple games aimed at building a secure attachment which is what he needs to be able to tolerate being without you - ie an internal model of knowing that people leave and come back again.
Work with the new childcare setting to have a very stable routine for him arriving and you leaving, so he always knows what happens at nursery, that will reduce his stress and help him cope. Lots of predictable, routine care so that he always knows what’s coming next.
I’m not at all surprised he’s struggling but please don’t think he’s trying to manipulate you or get his own way, at that age he’s just trying to feel safe, and he feels safe with you. The trick is to help him feel safe when you’re not there. Hang in there, I’ve done the “need to work, child not coping” thing - it’s very hard going.