I believe Trump will never concede the election.
The only model that can explain his behavior at this point is that Trump genuinely believes he is the victim of a concerted effort to depose him via electoral rigging, fraud, Deep State conspiracy, and/or any other means. It's not like he's entirely irrational in this belief, after all, he was impeached over circumstances surrounding the previous election.
I know comparing Trump to Hitler has become an overblown cliche at this point, but an interesting comparison can be made between Hitler's downfall and Trump's defeat. In the final days of WWII, Hitler struggled deeply with worthiness. He wondered if he was worthy to lead Germany. As the proverbial walls came crashing down around him, he never admitted his unworthiness, rather he said the German people were unworthy of him.
Likewise with Trump we see a man who fully believes he is worthy to lead America, and that his worthiness requires a 2nd term. Now that he has failed to secure a 2nd term, he must now confront his own unworthiness, which he is incapable of doing. And so, what we will see in the final days of the Trump administration is more and more blame shifting. We will see variations on this theme: "If the system wasn't rigged against me, I would've won."
If we do get a concession, it will likely be a reluctant one, nor will it acknowledge defeat in any sense. Trump will most likely say "In accordance with Constitutional Law, I am leaving office today." It will be a matter-of-fact statement that does not reference the results of the election at all. It will be unapologetic.
History will remember Trump as an aberration.