They did neuropsyc testing to see if the lack of ability to learn to put their own dishes in the dishwasher was a result of the medical issue. It was not. They are lucky and have very very minor complicications not related to this and that the NP believes could predate the medical issue.
Mild depression was mentioned. Treatment refused. Has a dx of ADHD, but a bad experience with one medication at age 5 and they refuse all treatment. Counseling has been declined.
Someone mentioned B12. They need a shot bwcause they are so low. The doctor is 1 block from the route they walk to work. It has been a month and no follow up. A single block. That is a literal block.
OK, so the B12 deficiency is huge. Lethargy, lack of focus, depression, are all symptoms of b12 deficiency. Pile that on top of untreated ADHD and I am not at all surprised this person is not functioning well.
You've mentioned that the person is capable of learning--I guess you mean they are capable of taking in and remembering information? That is only one small piece of being able to carry out something like loading a dishwasher. Executive function--our ability to organize, prioritize, initiate, and sustain activity--is quite separate from the ability to learn and retain information.
I've had ADHD my whole life, and most of that time have been unmedicated. My room was always a mess as a kid. My house is always a mess as an adult. I'm not lazy, and these days with a large family to take care of I work nearly constantly. But things are a mess because I can't work efficiently. I walk around the house with food because I can't sit in one place. I don't put my dishes in the dishwasher when I'm done with them because by the time I'm done eating my brain is somewhere else and "dishwasher" doesn't appear anywhere in my thought process. When I do load the dishwasher I do it haphazardly because that's what I can manage.
I do not have anxiety and depression issues. I have plenty of energy and will to do stuff. I just can't do stuff in an organized manner. I have to hire regular cleaning help to keep my house halfway descent.
My husband has chronic anxiety and depression. When he was unmedicated he went through periods when he could not bring himself to do anything at all. He would literally sit in a corner kind of curled up in a fetal position doing nothing for days on end.
While I recognize that you have limited ability to influence this person and that as long as they resist seeking treatment the best you can do may be to establish your own boundaries, I would be really reluctant to label the behavior you are seeing as lazy and manipulative when there are known physical issues affecting their energy and mental abilities.
(I'm leery of the lazy label because it is such a very common one applied to folks with ADHD by those who have never experienced what it is like to have a brain without strong executive function abilities)
Please know that I am not saying you just have to live with and tolerate a non functional adult in your household. But if there are underlying brain function problems it really is not helpful to presume that non functional behavior is just a choice. The person who is not functional may well need to go take their non functionality elsewhere so that your household can function.