Terrible toddler

My sisters middle son use to be this way as a toddler and up until he turned maybe 5 so like are 2-5 he’s 6 now and he goes and sees a behavioral therapist and it’s helped a lot. My sister was very scared at first but now she feels relieved. He also had selective mutism. Like he would talk to kids and friends and his parents but not to his teachers or other adults. But he’s also a middle child and my sister had babies every 2-2.5 years and had 3 and the pandemic happened when the older one was suppose to start school so all her plans to spend with him was shortened. My sister was also hard of hearing so it was frustrating for a child who whispers to communicate to get the attention of my sister without her hearing aids on. She was also extra nice to him and he would still act out.
From what I see on a lot of my mom groups it’s all normal toddler behavior believe it or not. What we think isn’t normal actually is, minus biting the cat. It could be a phase but consider therapy?

Some of this is normal toddler behavior besides hurting strangers and the cat. It seems a little over the top. Id suggest seeing a behavioral therapist. It seems to me like an emotional dysregulation. Like he is struggling to express his emotions without acting out

He’s already got a referral for trying to get behavioral therapist. They’re on a 3 year wait list unfortunately!! And he doesn’t bite and smack just because he doesn’t get his way he bites and smacks just out of randomness. We could not be doing anything and he’ll just come up and full fledge smack! It’s not normal toddler behavior, he genuinely has issues and I’m struggling to get help for it.

Can you see an occupational therapist? They may be able to help as well.

Does he show emotions when he bites and smacks? Only because my child found it still finds it hard to balance emotions when he gets to excited he randomly bites but it's like he doesn't know what to do with excitement and when he hits his not always angry it's like a random moment his 4 now and still does the random attacks and biting but its not all anger sometimes yes but not always I've made him emotions cards to try and let us and himself know how his feeling before the occurrence starts so we know in advance