I cannot recommend "The Explosive Child" by Ross Greene highly enough.
I understand why you are so overwhelmed OP. Did ALL of this behaviour start with school? Has he been otherwise developmentally typical both socially and in private?
He sounds very like me if I'm honest. I have PDA, a profile of Autism and CPTSD from complex childhood trauma.
I think in the short term while making contact with help you must stop punishments/time outs etc. He is hugely emotionally dysregulated (for whatever reason that may be) and despite the fact it's a very 'typical parent' response and completely understandable - it's not helping him or you.
There is a lot to unpack here and you need professional help. What you said about his reaction to dinner strikes a chord with me - this is a typical reaction in a child with inexplicably and unmanageably high anxiety. Anxiety so high any decision making must be done completely autonomously and without pressure and all requests/questions feel like pressure (to answer).
How often are these meltdowns in response to a request, question or change in task? Does he have any control over himself during? Does he acknowledge his behaviour afterwards at all?
Reframe these away from tantrums for now, these are not tantrums. Reframe what's really needed short term (as someone said above about are shopping trips needed). This is important, and much easier in principle than practice. But not everything matters and giving in is NOT ALWAYS WRONG. Something is wrong already, and adjusting expectations of him to be as minimal as possible in the meantime might help with the outbursts.