What exactly are you talking about? To prove WHAT exactly?
I don't know of anyone who says SOMETHING did not happen, but the devil is always in the details.
There were many falsities and even downright lies about what happened. I am actually curious about why this is so exaggerated when it was bad enough to begin with.
For example, there once were stories about Jews being made into lampshades. This was patently false. There was one woman the prosecution attempted to link to the lampshades, but that was readily dismissed.
There was another silly story about making soap out of the fat of Jews. This was also dismissed.
One of the more ridiculous stories concerned roller coasters dumping Jews into gas chambers (see story below).
These stories were once accepted, but then debunked. How did they get debunked? Someone must first question them. Then, there is investigation. Evidence is gathered. A conclusion is reached. A theory is debunked.
Today, there is gathering evidence about whether the gas chambers were intentionally built for the express purpose of gassing victims to death. Evidence is now surfacing that the gas chambers were actually delousing stations. Lice was rampant in the labor camps, so new arrivals were immediately sent into one of these buildings. Many got sick from the poison and even died. It goes without say that this is horrible and inhuman, so why the need to exaggerate something that was so terrible to begin with? I actually think that eyewitnesses saw people entering the delousing stations, get sick, and then assumed the intent was to just kill them. These however, were actually labor camps. You don't purposely kill your own labor. Everyone was made to do something. And yes, sick and feeble people were mercilessly allowed to die, which is also horrible in and of itself.
Today's environment is often hostile to free speech. You can be put in jail in certain European countries for any slight deviation from the official narrative of the Jewish genocide. If that intolerance existed several years ago, then we might have never learned about the absurdity of lampshades, soap, and roller coasters.
I am hardly a Nazi sympathizer, but I do question much of ANYTHING in history or on the news that I run across (I am sure you are familiar with the term "fake news." Certain subjects however, seem to be taboo from intolerant people. Using of the word "denial" is therefore, a false dichotomy. It's not as if people claim that NOTHING happened.
Look at the replies to your question. Many knee jerk reactions and insults. There is no desire for thoughtful investigation.
Here is the quote about the gas chamber roller coaster (see comments)