I sometimes get sick of parents who tell me he’d eat what was on their table or he wouldn’t eat
Too many parents make the assumption that what works for their child would work for all children. Try to ignore them.
You can't win if you're trying to persuade a child to eat something they don't want to eat. All you can do is focus on not making the issue any bigger. Find ways to make mealtimes more relaxed. Food issues are just made worse when people are stressed about them.
Make the food he likes, prepare other food too and make sure it's available.
Don't comment on what he does or doesn't eat. That includes that miracle occasion when he first tries something new. Commenting/celebrating/rewarding could stop him feeling able to do it again.
At mealtimes, talk about everything apart from food.
You've found a way to reduce the stress at the weekends so try to make sure that there are a few different options available for grazing. Don't comment on them or push them: just put them out.
Above all, remember that pressure to eat is what is most likely to reduce how much he eats and cause him to lose weight. It isn't your role to persuade him to eat. It's your role to make a reasonable balance of food available and let him select from that what to put in his own mouth.
Please don't cook him any more meals that he won't be able to eat. That will just distress both of you and achieve nothing.
My DD2 was like this and it nearly killed me being laid back and not commenting. She still reacts badly to pressure to eat aged 15 but freedom to lead her own progress means that she has a much healthier and more normal diet now and mealtimes in our house are pleasant, social occasion that everyone enjoys.