You have that precisely backward. Trump is the first defeated Presidential candidate in the history of the republic to permanently persuade his voters he was the one elected. Among the several nail biter elections, which Biden's victory was not, the closest was in 1824 when the incumbent Andrew Jackson won the popular vote but tied in the electoral college with John Quincy Adams. The House of Representatives then gave the Presidency to Adams in a party line vote. That January, before the inauguration, a Washington birthday party was held for the aging Lafayette, who crossed the Atlantic to attend. Both Adams and the soon to be outgoing President were there, their first time in the same room since the election. Jackson walked up to Adams and shook his hand, congratulating him on his victory.
At the party was the artist, Samuel Morse, one day to be inventor of the telegraph, who witnessed the handshake and recounted it in a letter to his wife. Concluded Morse:
"The President takes his defeat like a man"
(Read about this in "The Greater Journey" by David McCullough. Seems a lesson for our time.)