I absolutely can not stand it when I see things like “I am terrified of my child, they are causing me PTSD” and in no way shape or form, are they exaggerating.
You are the parent, so do your job. You are forever the one in a position of power, as long as your child is legally your responsibility. You are the one that can take valuables away from them (cell phones, games, pcs/laptops, television, etc). You are the one who can give them time outs. You are the one who can give them a disciplinary spanking (which is different from beating a kid’s butt out of anger).
Unfortunately, there’s “one discipline” that works for every child. There are parenting classes out there, if you feel like you need to be formally taught (and/or are curious about how to handle a situation). Udemy offers courses online on parenting (the cheapest I have found on this website are 10 US dollars).
There is also counseling, to better understand both yourself and your child (or children). Children are basically like puppies up to a certain age, where often times the use of your voice in specific ways (harsh, gentle, soothing, etc) is just enough to get a child to do what you want (calm down from crying, stop them from doing something that will hurt them, etc).
Counseling can also be beneficial, because if there is underlying problems going on (reactive attachment disorder, anxiety disorder, deviance towards authority, etc) it can help figure out the root of the problem, and better help treat the symptoms.
There is no shame in asking a counselor for help, especially if you feel like you are at the end of your rope. Heck, even counselors have counselors to help themselves.
The morale of the story? You are a parent, so please do your job and parent your child. Your child should never be the one “calling the shots” in your household. You are the one with the power and the control in your household.