I've had various questions over the years about this thread. Our daughter was eventually properly diagnosed by CAMHS as autistic, and we completely changed our way of parenting her. After getting advice on Mumsnet, we started to use low-demand techniques, and this was a real breakthrough for us. Once we started to 'parent' her less, her behaviour calmed down (ok, not every day and not straight away!) We learned not to react - even when the house was getting smashed up! We just let it happen, and she did not continue once she realised we were not going to intervene. However, we suffered a few holes in the walls and repair bills, but it was worth toughing it out.
Her primary school were absolutely no help, and because she was so perfectly behaved, they completely gaslighted me whenever I raised concerns. We went back to see a GP, who thankfully understood about girls masking anxiety and re-engaged CAMHS. It took years to get her to participate in CBT, though, and I'm not sure if this made much difference anyway. However, the low-demand stuff really works. I would suggest giving it a go; if your explosive child responds well, this could be an indicator they are autistic or have PDA.
My daughter is so well-behaved outside of the house that most people still give us the impression we must be making it up if we ever mention her diagnosis. But we know, and that's what counts. We have experienced how much her diagnosis has improved all our lives.
I wish I had noticed earlier that my daughter's tantrums were not about her asking for things EVER; they were always about her getting away or NOT wanting things, such as noise, other people, changing clothes, etc. Once I realised this, thanks to help from Mumsnetters, things finally started to add up. It was not me parenting badly; I was just using neurotypical techniques on a neurodiverse child. I just needed to understand her triggers, get her to understand them and steer her own way through them.
I hope this helps those of you having similar struggles. Good luck!