We can't help anyone who doesn't want help, especially when they're 18 and an adult. My nearly 18 yo grandchild lives with me. My counselor said I have to let go and allow them to have the natural consequences that happen when they make poor decisions. Consequences given by life and not by me. I still give consequences for actions related to boundaries I set for her to live in my house. The ones I focus the most on is no smoking pot or cigarettes or drinking alcohol in my house and doors are to be left open. I've confiscated bongs. They do comply with doors open. She has dropped school. I expect that she'll pick it up when she experiences difficulty getting a well paying job once she starts having to pay rent. Natural consequences will teach much better than my lectures and my anger.
Your son's school work is his responsibility. Tell him that you're not going to be involved with school issues. Same for the responsibilities at home. Doesn't feed and water the dog; the dog goes away. If you want to keep the dog, you take over that chore. It's not a hill to die on.You can't make him do it.
For him to learn, consequences have to fit the "crime." It's also your responsibility to take care of you. Do not give him a consequence that interferes with your life. If you want to keep the dog, you feed and water him.
I suggest nothing is working as far as your consequences go, because you've become personally invested, spending hours trying to force him to do as you say. It's become a power struggle during which you seem to have all the power. His normal reaction is to not do what you ask. This gives him power over you. I suggest, based on personal experience with my siblings, my daughter and my grandchildren, that you let go. Allow him to make decisions about the things that directly affect him. For example, school.
As for him not doing chores to meet your standards stop trying to force him to do them right. As you see it isn't working to correct him. Just say in a calm neutral voice, "thank you for doing it" and ignore the rest. I learned this with my daughter. She was unwilling to follow my directions. Both of us were angry. She was 7yo and difficult. I started giving her the responsibility of doing the chore. I didn't stay in the room and I didn't complain about her sloppy job. Eventually, once she knew that this was unimportant to me, she improved her way of doing the chore. And....I eventually realized my relationship with her was more important than chores done "right." I focused on building a positive relationship by thanking her when she made an effort to do a chore.
I listened more than talked. We had casual conversations about what we would do that included both fun activities and chores together. We talked about her interests. I bought the crafts she wanted to do.
Making that change was definitely not easy. I found help and support from a counselor. I suggest you get help in turning around your negative relationship with your son. You're in a battle with him. A battle in which neither one of you will win. Both of you are angry. You cannot force him into counseling but you can get counseling that will help you learn a way to live with less anger.
I seriously recommend reading the book Love and Logic for Teens. Love and Logic have a couple of web sites that will give you information about parenting.
Once I focused on finding happiness for me without expecting anything from her, I was happier and my relationship with my adult daughter gradually changed.
I also had counseling focused on the way I depended on others to be happy. If suggest you read about co-dependence. There are several helpful books.
Of course you want your son to be successful. You worry. You feel like a failure. You're angry because he isn't listening to you while you see him failing. You desperately want him to be responsible. You cannot change him with lectures and consequences. You tried that and it's not working. However, once he realizes that he, alone, is responsible for himself, he is more likely to eventually change. You have to let him suffer the consequences; to stop trying to protect him from the life you see for him. I suggest taking your focus off him and onto your self in ways that will give you satisfaction. Give your son responsibility for his life.