Reading your other thread I can see why you are giving up on schoolwork. Parents are the main influence in a young person's life. Good ones love their children, see them as persons and play to their strengths, be it football, music, reading, pets or whatever -and are consistent - important.
You are secure and happy. True they make mistakes, but by and large it is good. you end up confident and can deal with the upsets you find in life.
Sadly that's not you. Your parents had expectations that echoed their own ambitions, and blew hot and cold, abusing and insulting you, threatening you, then backing off for a bit, before coming back worse. Never seeing you as a person, with strengths and abilities -simply becuse you were not an echo of them.
You ended up injured, which comes out as not believing in yourself -or anything much. Seeing nothing ahead.
Their behavior is destructive and has injured you, leaving you feeling you have failed and cannot face failing again. Never believing in yourself -or anything much.
The world is bigger than your parents, it is bigger than the future you see for yourself. Success is not always schoolwork, it comes in all shapes and sizes, simply being kind to others can be the best success of all - and that's nothing to do with a job or academic papers. Success can be in appreciating something, possibly art, possibly animals, possibly ... well just about anything you care to imagine.
What could yours be?
One success for me was using my parent's actions and beliefs as how not to bring up my offspring, so I did the opposite -it worked.
Trying to get that injury healed - so you can find things in life to reach out for - is not a solo job. I could never make myself better, and became worse as time went on. It was only when I did have competent and caring medical support did I start to improve. Now I have the confidence to take on tasks, talk with people and be a parent and partner. I'd not have believed it possible when I was a lot younger.
If you can't get better by yourself I guess that means you need assistance. And that's a problem as you do not feel you can open up.
Can I suggest you start out with the chat line at Kids Help Line. No talking on the phone or face to face, a bit like here -all text.
It would be a start, and can lead to better things.
I'd like to let you find 18 can be a door, not a dead end
Would you like you like to talk some more?