What do I do about my undisciplined little brother? He is starting to show really troubling behavior

I am 21, and my brother is 13. I currently live at home, as it is pretty much impossible to afford living on my own at this moment and living with a friend or having a roommate is not an option either.
My brother has always been a pretty wild kid. He actually finally got diagnosed with ADHD a few months ago, and the medication has done wonders for him. He does really good in school, and is super talented and smart and is overall a good kid. However, he absolutely has behavioral issues that my parents just have not addressed or attempted to fix in a real way. This has been an ongoing issue for many years, but as he has gotten older it has just gotten so much worse. He has a habit of getting incredibly angry at his video games, and ends up yelling at the game or anyone around him and even breaking electronics. Despite this, he has literally never been grounded, not once. My parents will blow up at him and there will be a whole screaming match for a while, but after he cools down they just hand him everything back until it happens again. He can be rough with his laptops when playing, and on average goes through a computer a year. If I could give numbers I’d say he’s gone through 4 laptops and 5 kindle tablets since he was like 6, always getting a new one within weeks to days. He has been given unlimited electronic access since he could basically talk and this definitely has not helped a bit either. But I’m getting so incredibly fed up with this constant cycle of him being out of control and nothing ever being done about it. He’s started to get physical too which is really starting to worry me.
Just this morning I woke up to him and my mom going at it because he was refusing to get up for school and was playing on his computer instead. My mom closed the laptop turning off whatever he was doing, and in response he started kicking and punching her, and calling her things like “you stupid fat f-ing b-ch” and “c-nt”. That second one is a huge nono for her, and finally after it was uttered she threatened to take his phone. This made him even angrier and he started running around kicking and throwing things, saying over and over “what did I do?” “I didn’t do anything” (this is really common for him to do after acting out) But still throughout this whole thing, he still has his phone, and her just threatening to take it but not actually falling through. This has been going on for years, but the physical stuff is pretty new. He’s even threatened to stab himself or someone else, I had to run and beat him to the kitchen drawer once because he was going for a knife and hold him back and try to calm him down. I feel like the most simple resolution to this is to take away electronic privileges even for like a week and lay down actual punishments for out of control behavior, but whenever I try bringing this up my parents just say he won’t listen and it won’t work because he’ll just make life a living hell for us until he gets what he wants. I really don’t get why they let him get away with so much. When I was way younger than him, I faced actual punishments and I really wouldn’t even do much to receive them. Tablets taken away for weeks or my phone being thrown out of the second story window for a C minus or lying about doing my homework type stuff. If I acted the way he did I think I would have actually been beaten. And in no way do I think that’s what they should do, I’m just at a loss of what I can do or say to bring about actual change for his behavior. I don’t make enough money to move out, and none of my friends are looking to room together. I live in a super rural area too so finding roommates I don’t know would be incredibly tough.
I feel really stuck, and want to help him but I also really need to just get out of this house too. I don’t even have my own car so I can’t leave when things get intense, just hide out in my room. Every time I try intervening I’m told I’m not his parent and to stay out of it. I think he needs therapy bad too but it took me getting hospitalized in my teens for my parents to finally take my mental health seriously. I am just at such a loss on how to go about this.