My husband diagnosed with Alzheimer's sleeps all day. He recovered from Covid and has no motivation to exercise or help me. Any advice?

I’d suspect long Covid because I know others who had Covid and the long effect is something like you describe. With one friend, the Covid was a mild case and he thought he was fine afterward. Ask his doctor if long Covid is a possibility because there might be some treatment that could help your husband. Research is still developing with long Covid. (And if you are reading this post, I want to reiterate that the pandemic is not over. Please mask properly and observe precautions because Covid is not “just a cold.”

This is a very sudden change if your husband was two weeks ago driving to fitness centers.
I would discuss with the doctor. You may be looking at long Covid, and if so this may take some time to recover from.
Discuss this sudden change with your husband's doctor. As to his "help" it is real clear you won't be getting that for a while, so you will need to work around that somehow.
I agree with JoAnn about vitamins. They often are not a "benign treatment" and they can cause problems. They are not regulated in any way. They can cause problems. Try for as balanced a diet as you can and perhaps one multivitamin, which, tests show, pretty much wash right out in the urine. The body does not absorb benefits from vitamins in the same way it does from food. They were right about that Chicken Soup all along.
Wishing you the best and hoping you will update as you go.

Are these vitamins OKd by his doctor. Taking too many can cause problems and interact with his meds.

COVID can have lasting effects. Maybe he should be taken off of some of his meds. Those that help with cognitively do no good after a Dementia progresses. Take a list of your concerns to tge doctors with you. Only he can remove the meds and add new ones.