FWIW, I largely agree with this Vox analysis of Biden's interview.

https://www.vox.com/politics/359160/biden-abc-news-interview-drop-out

He did better than in the debate, but not well enough to quell the serious doubts about his mental state, and his ability to beat Trump.

In some cases, where the Vox article suggests he's delusional (e.g. - denying he has a low approval rating and that he is now trailing Trump more than before), he could actually just be lying. But in that event, he would have to believe these lies would work, which is also not reassuring. Political lies do work quite often, but this is unlikely to be one of those times, as the people he needs to persuade on this point are Democratic elites and relatively well-informed voters who know what the polling says.