Hello @Daddd
it's incredibly difficult and I don't have any magic wands sadly. We are in the middle of this with my older child, who's a few years ahead of yours. Shouting, swearing at me, endlessly breaking the rules, deceptiveness around screens. He does have a good heart but the form his autism takes creates a lot of challenges. We walk on eggshells.
Mainly the key is to be consistent, consistent, consistent ... which is far easier said than done. I hope that in the end he will internalize our not-very-demanding rules.
Also we have external help from an autism support centre. The guy comes once every week or two weeks, depending. He worked by talking to my eldest and establishing a rapport, then gradually in a very low key way encouraging more desirable behaviour. We have had some terrible flashpoints and explosions but the support worker helps a lot.
We also have rules (agreed when Support Worker, son and I sat together formally) and he needs to follow the rules or he gets a cross. Three crosses and no gaming for a week. Applying the rules is bloody difficult though as the explosiveness is extremely hard to handle.
Is there any chance of getting some help like we have? Every sympathy - walking on eggshells and being afraid of your own son is a bad way to live.
Agreed with other posters that his room may well be his safe space. But that doesn't mean he can just ignore what you say. We have ended up communicating with son more through Discord than talking :s
We also have the ability to turn off his internet access. That helped massively - if you say 'time to stop now and go to bed', it was huge arguments. If you say "fifteen minutes then the internet goes out" he accepts it better .... Mostly. Notably he copes better when given a 15 or 30 minute warning for anything than when he isn't. The bigger the event, the longer he needs the warning.
You say you work in the field, so maybe you know all this already. But I hope something will help.
Again, every sympathy. It's extremely difficult when this goes on and on and on.
There is a parenting special needs board on Mumsnet, maybe there's some help there too.