If an elder has no insight into the degree of their dementia, is there any way or hope of explaining that to them?

Forget trying to convince your father, it is a total waste of time, just another downward step into the abyss of dementia.

You are trying too hard to bring him back to normal understanding, won't work.

Some people with dementia know they have it. My mother knew and answered every question with Ask my daughter. She's my brain. But others think they remember just fine and it's not worth the arguments or confusion to try to convince them otherwise. Most people with dementia remember the past well and it's the short term that is a problem for them. They don't retain new information.

I it's like explaining the birds and bee's to kids, you do it on there age level. You don't explain to a 5 year things they can't possibly understand for there age.

So if they ask explain it on a level that there cognitive decline is. Make it brief and change the subject.

Otherwise I wouldn't.

Better not to discuss it - Just frustrates them .

Sometimes.
That is to say there are days you can speak with them about it better than other days.

My brother was diagnosed, after a car accident, with "probable early Lewy's dementia". He was diagnosed by symptoms he described for the doctors. Scans showed little. He was at the time living on his own, with me at the other end of our long state.
I had already started to notice a difference in his hand writing, but his long letters were still good. Then, when we talked on the phone suddenly he wasn't there. He said it was his phone. Phone company said phone was fine. Odd things. I went to visit and he wasn't eating as well. Was more thin. Suddenly HATED grocery shopping. Said store was ''too big; too much stuff" (it kind of was) In the evening, one cocktail and he was gone--kind of silly. Not much else. Poor balance. Vivid dreams he could remember and believed he was awake when having them (he was having first hallucinations).

Then the call about the accident from the hospital. He was still so seemingly "with it". Got together with his attorney. Make me POA and made me Trustee. Said he KNEW something was happening before it happened, but throught it was "other stuff; the phone company's fault, etc". Worried more about his own driving skills. That sort of thing. Dreams that happened when awake. Knew he needed to go where he "was safe" (ALF).

We would often talk. He would say what he saw and I would say what I saw and he KNEW he wasn't seeing it right. We got him into a good assisted living. He could talk about being afraid of what was coming, but said he was glad to know why he saw the world so messed up. He was glad to know he had dementia and it wasn't his fault. But he dreaded the loss of all control.

Much as we could reason and talk, more and more we could NOT. He began to get paranoid. Thought someone stole from him. Couldn't be reasoned with tho he was wrong. Hid things. Had hallucinations he now thought not a dream, but real.

So sometimes he could grasp things and sometimes he could not, and it was worsening. He died of sepsis before it could get him, and he was happy about that while in hospice his last days at the beginning of Covid.

For a while I think, in the beginning for many people, is "good days" and "bad days". The latter become the more common. It all becomes slowly worse, and then it speeds up. And on you go.

Different perhaps in each case. I always say it's as individual as our own thumbprint.

Strugglinson, I have seen this progression from knowing, acknowledging to denial, it is common I think.

Try to not have those conversations, they do no good because your dad's brain is now unable to see his deficiencies, this to shall pass in time.

In an entirely different set of circumstances, my adult son has a brain injury from complications of a birth defect. He has had extensive neuropsych testing several times which consistently indicates poor insight, very little reasoning skills, short term memory loss, and executive planning skill loss. He knows but also doesn’t know that he has some challenges. He fights hard any attempt to control his choices and would completely reject any explanation of his condition. Your dad is much the same. Believe me, on some level he knows there’s an issue, a big one. Trying to explain or convince him of it is an exercise in futility and also a bit unintentionally cruel. It doesn’t really matter, it changes nothing. Differing from my son, sadly your dad’s condition will worsen. He’s the best he will be right now. A friend once told me acceptance is a gift you give yourself. I wish this for you, as I know it’s so very hard

Trying to get someone with dementia to realize they have it is not worth attempting to do.

He will never accept that he has dementia. All that will happen if you try to explain will be a fight. It's not worth it.

If the doctor has made a diagnosis, hopefully you have an active POA and can start making the decisions before your father makes a mess that you will be stuck trying to cleaning up.