They ALL knew about it.
The hope was Biden was going to die in office.
I do believe that was the plan. And it he died after the first two years then Kamala could serve two more whole terms as well as the rest of his term.
Then it became evident that she was a total nitwit herself. The plan was to get rid of her the second term and hope he dies then, so the new vice president can take over.
Instead he was forced out and being the vindictive bastard he is, he endorsed Harris, knowing full well, nobody really wanted her, but being a black woman, they were stuck with her.