Welcome, EvenStephen.
Perhaps cleaning his room doesn't make sense to him. I learned to curtail meltdowns by telling my son, "Today I want you to remove all of your white socks and any other white clothing or sheets lying around on your bedroom floor, and put them all in the washing machine. Turn on the washing machine with hot water and use 1/2 cup of soap. (I had to wait until he was tall enough, which was about 5 yrs old. Your son is tall enough I assume.)
"Clean your room" sounds like "Clean up all terrorism in the Middle East" to a kid with-ADHD and ODD.

The next day, it's "Today I want you to spray Green Clean on your floor, wipe it up with paper towels, and throw away the paper towels. Then pick up and throw away all glasses and cans in your room. Be sure to dump them in the sink first."
After a few months of that, he caught on that he was actually cleaning his room, lol!
In regard to cleaning his body, he may have sensory issues. Does he hate showers? My son wouldn't shower until he was nearly a teenager. But he was fine in the tub with toys.
He also had a lot of issues with-going to the bathroom and cleaning up. Imagine an out-of-control toddler in a 10-yr-old's body. Ew.
So I bought WetWipes (made sure there was no baby picture on it!) and showed him how to use them.
Just a couple of ideas.