Oh no, I'm so sorry you're going through this experience! It is so hard when you add another person to the family and the last person you added feels like it's a slight against them. I have three so I feel you, each addition created new challenges while adding to the love in our family.
Now, what to do. It is going to seem counter-intuitive but this behaviour is a cry for your love and attention. I know, why would you behave like a monster to bring people closer to you? Well, children lack emotional regulation. What they need from us is calm reassurance that their storm of emotions is okay and we will help them manage those.
It is also going to seem like you're letting him get away with yelling and arguing and talking back and punching and all sorts if you take him in your arms and comfort him. But, that's what I'm going to ask you to do. Every time he carries on like, as my father would say, a 'pork chop', he's actually asking you to show him how much you love him.
His behaviour is a way of connecting, it's not very nice or effective, but it's also a way of releasing his strong emotions. He may be feeling left out, less loved and will certainly have to compete with the very real needs of a 4 week old baby. It's likely his behaviour is a way of showing that. He's had you all to himself for three and a half years, now he has to share you with this interloper that doesn't appear to be going whence it came.
So, try to give him some more obvious love, and draw attention to that love. You can do that by giving him some more one on one time and give him lots of hugs when he acts up. There's a trite expression in the positive parenting literature that children spell love t-i-m-e. He's asking for your time to show your love and affection, even if he's going about it a very strange way to adult eyes.