For those who think he'll never concede-- you might be surprised. Narcissists will concede or apologize if it's in their best interest and they really have no other options.
But it won't be the real, gracious concession people are hoping for. It'll be completely disingenuous and full of caveats. Narcissists say non-apology, blame-shifting things like "I'm sorry if you were were offended by what I said", instead of an actual apology "I'm sorry for what I said".
In his case, he'll likely admit that technically Joe has been elected. But, it's a sham. It was done with illegal votes. There was widespread fraud. He was robbed. The American people are being robbed. This is the corrupt system he was warning about and fighting for the people. Etc etc. You know the drill.
It'll be wholly unsatisfying.