He did pick up on the Putin gaffe and immediately corrected himself and explained that his enemies have been on his mind lately.

He didn’t correct calling Kamala Harris Trump.

He’s been known for making gaffes since he was Obama’s vice president. From his Wikipedia page:

The remark revived Biden’s reputation for gaffes.[227][221][228]

Those sources are from 2009.

Journalist and TV anchor Wolf Blitzer has called Biden loquacious;[692] journalist Mark Bowden has said that he is famous for “talking too much”, leaning in close “like an old pal with something urgent to tell you”.[298] He often deviates from prepared remarks[693] and sometimes “puts his foot in his mouth”.[169][694][695] Biden has a reputation for being prone to gaffes[696] and in 2018 called himself “a gaffe machine”.[697][698] The New York Times wrote that Biden’s “weak filters make him capable of blurting out pretty much anything.”[169]

He has struggled with a stutter most of his life, which he learned to cover up.