My firstborn was hard work and quite unpleasant up until the age of 4.
He was angry about everything, tantrummed about everything. He would kick, hit and spit at me.
This was back in the supernanny days. And although people love to hate her, we found her style worked. Clear boundaries. Time out. Though this ended up with me sitting outside his bedroom holding the door shut as he would come and hit/kick/spit at me. But it worked. Every time he just needed zero stimulation to calm down. Hugs didn't work, reasoning with him didn't work. He just needed time by himself.
It was awful. His whole baby and toddlerhood was awful. People would comment on it when we were out. My friends with other babies would comment - which was helpful on those days when I'd think it was me.
When he was about 3 and really violent I'd worry about this continuing when he was 15 and how he'd be able to really hurt me or someone else.
But it passed.
He's a teenager now and good as gold (so far). He calmed right down around age 4. Had some wobbles in primary (but the pandemic meant he had the opportunity to learn some self motivation and self discipline).
He still had his moments, but we all know the drill. He goes upstairs and has some time alone, and some time later it passes and we're all good again.
'Validating his feelings' and all the talking we're encouraged to do these days just doesn't work for him. It makes him spiral.
We're now having a similar thing with our youngest (8), but this focus on emotions at school is really causing him a problem. Ironically,
OP, you have my sympathy. I know it's not popular now but do try some firm boundaries. Hopefully like us it'll get better for you soon.
(We haven't had any ND suggested, but there are clear traits in the family.)