First of all your resentment is understandable.
Adhd is not a disability it is more of difference in thinking that stems from difference in serotonin production.
Reading your description sounds like people have been taking care of him and he hasn’t learned to be totally self sufficient. It is possible for him to be self sufficient. However the methods of teaching that need to be adjusted. Direct him with clear short direction. For example please gather the dishes and clean them everyday. Remind him to do them as needed remind him to clear the food from the sink.
Remind him to study for that test if there is real opportunity for him.
I am a 44 years old who was diagnosed at 42 clearly I made to a good job and house and family yet I still struggle and I know everyone struggles as well.