My brother met him in an informal setting about two years ago, and expressed concern then over "wow he seemed really old / out of it". But Biden's current speeches and interviews seem lucid and coherent so maybe he was just having a bad day back then.

The presidency, like most other executive jobs, ends up being run by a team of people working together behind the public figurehead. I have faith in Kamala, in the White House advisors, in the picks for cabinet positions, etc. Biden will probably invite back many Obama-era advisors, as opposed to white nationalists like Stephen Miller. Decent people tend to build decent organizations.