His whole image is built around Soviet style "stongman" cult of personality. Everything he says is planned beforehand like his annual Q&As on state media channel where people in the audience just ask him pre-selected questions and he answers them in the most "based and redpilled" ways possible to make him look cool and strong. They're basically all the same every year.
His whole image is built around this idea of how strong he is. From his cringe shirtless photoshoots in nature and diving naked into freezing water to him threatening almost every year to punish any country that "mistreated" Russia or questioning another country's sovereignty like Kazakhstan, Ukraine or even Belarus.
He does all of this because he knows that it appeals to the numerous lower class people (vatnik) that miss the USSR and need a daddy figure after so many years of being ruled by one.
Everything is just a mirage and right now he's in the most vulnerable state he's ever been. The ruble is shambles, his covid response was absolutely abysmal, millions of Russians are jobless because of virus, he increased the retirement age which caused many of his die hard boomers to turn against him, the whole Navalny saga helped shatter his anti-corruption imagine that some russians had of him, he got completely alienated in the international stage and the whole economy is pretty much in stagnation.
This whole "debate with Biden" saga is just another attempt at showing how cool and strong and it all coincides with russian state media talking 24/7 about how Biden is frail and has dementia unlike glorious leader Putin.