In France Presidential election in 2002, right-extremist Front National's Jean-Marie Le Pen shockingly qualified for the second round against incumbent right-wing RPR's Jacques Chirac.
Jacques Chirac then refused to participate in the traditionnal debate between the two finalists, that was due to happen five days before the final vote. Chirac stated reason was to deny a platform to Le Pen's hate speach. More prosaically, he also had nothing to win by facing Le Pen's critics and aggresive rhetorics while all opinion surveys (and huge anti-Le Pen demonstrations) predicted a large Chirac's victory.
Indeed, the electors didn't blame Chirac for the canceled debate and he was reelected with the largest margin in French 5th Republic's history, 82% to 18%.
Take it with all the salt of the Atlantic Ocean that separates the two countries and their political cultures, but one could argue that Chirac (establishment, held various offices for 30 years, right-wing in France which might be associated with centrists/moderates in the USA...) vs Le Pen (populist, far-right, militarist, anti-abortion...) in 2002 was a similar political configuration as Biden vs Trump 2020.
Notably, in a similar configuration in 2017 when he was facing Jean-Marie Le Pen's daughter Marine Le Pen, then-centrist Emmanuel Macron accepted to debate with her. He won the debate according to all media reports - later his opponent admitted it herself, and he acceded to the French Presidency.