Pre lock down the local chip shop had a job advertised for two hours a day during school times, I thought it’d be a way of seeing how I managed working again. His response to me saying I might apply was to point out I’m crap at maths and will struggle then say he couldn’t take time off during the holidays so what would I do then
This is the classic (in my opinion abusive) stance men take when they don't want the woman to stop facilitating their job.
You are just as entitled to work outside of the home as he is. (And this job sounds like it would have been perfect - 2 hours during school time would be great solution).
The child has two parents. Both of whom are capable of looking after him.
Half of the childcare is your DH's responsibility, even during school holidays. At the moment you're choosing to cover it all. But if you want to work instead, then DH can no longer push his half of the childcare responsibility onto you. You'll need to sit down together and discuss options and how you can solve the problem.
At present, you're making 100% of the career sacrifice. Your DH is making 0%. By demanding that you never require him to cover a day of school holidays (or evenings, or weekends), he's making it completely impossible for you to work. And he knows it.
He sounds like a nasty piece of work. Whispering doubts into your ear about whether you can cope with the work, telling you that your child is your sole responsibility, vetoing the idea of you doing evening or weekend work because he might have to do some childcare. He wants you at home dealing with the childcare and the housework so he doesn't have to.
I bet you're far more capable of holding down a job than you think you are. If you didn't have his negative influence grinding down your confidence, and instead he was positive and encouraging and supportive... I reckon you might find you could work your way into a job you enjoyed and actually be good at.