I have a theory about Whyman:

Something happened on earth that endangered the lives of all mankind, and Whyman petrified humanity to save it.

And that's why the jellyfish cures any disease and defies death.

And the "do you want to die?" Phase. Not to be a threat, and in fact Whyman not sure if the jellyfish also cures that disease?

My assumption would be that either is a kind of government project, made to save humanity from one of two types of catastrophes: 1) stopping a nuclear war (which could destroy the earth) 2) stopping the sending of radio waves throughout the universe ( if aliens are involved or something similar); for 2) I would understand the man's almost angry reaction why when Senku started sending radio waves again. I guess it could be a desperate measure to stop global warming, or the release of a virus (biological warfare instead of nuclear), and my last theory: an experiment out of control that would explain the gigantic number of jellyfish discovered in America. and birds used as guinea pigs). As Senku's voice used, probably some kind of artificial intelligence is still active, with the computer located on the moon (thus protected from the changing earth and the solar energy source), maybe that system was programmed to bring humanity back to life after fulfilling the purpose of the mission, and now Senku has introduced errors in the system. I would have been surprised if all my ideas were wrong (in an elegant and logical way as the whole series has been so far).

"As Senku's voice used, there's probably still some kind of artificial intelligence still active, with the computer located on the moon." I think that artificial intelligence would actually be Mecha Senku.