Biden has spent more time than any other president at his private residences & when he is there he hides in his house. He just finished another 4 day weekend. His normal workweek ends early Friday & sometimes on Thursdays. His rare public appearances are scripted (speeches only a few minutes) & he rarely takes questions. When he does take questions, they are from selected reporters & other times the answers are yes/no.
Very often his scripted speeches wander off into incoherent mumbling. There are numerous videos of him him wandering off & he can't climb stairs.
I think the reason why he hasn't announced is that the puppet masters are trying to decide if he is even healthy enough to make an occasional campaign speech & give an appearance of running the country. Meanwhile the democrats are trying to figure out who else to run.