Bad behavior after baby 2

My toddler is on my last nerve after we had baby 2. I’m doing everything they say to do. Asking him to help, brought him his own presents, give him tons of one-on-one time, let him eat pretty much what he wants right now to try and avoid meltdowns, taking him outside, doing special activities with him…and he’s still acting like a complete maniac. He will literally just stand there shouting no at me for an hour. He’s taken to hitting and spitting. He throws tantrums over the most minuscule things. I tried to tell him he can stomp his foot when he’s mad instead of hitting me and I kid you not he looked me dead in the eye and smacked me. He refuses to even look at his sister. He’s making it so hard to be his parent and I’m literally ripping my hair out trying to figure him out. I don’t understand and I’m so sad over it. I also feel like it’s causing me to have not enough bonding time with the baby. Did anyone else experience this and have you found anything to help? Not loving being a mom these days 🥺