When you die, your Humanoid enters a Death State where you
cannot change any of the Values. If you wanna make your Character
Jump even after he dies you’ll need to make a separate script where maybe you could use UserInputService or make the Humanoid not die.
For example: Make him enter a ragdoll state or something like that, code your own logic for it.
You can use bodyvelocity to simulate jumping physical
Example:
Every time the input space is pressed, you check if humanoid.FloorMaterial ~= Enum.Material.Air, and then you create a bodyvelocity with Velocity = Vector3.new(0,1,0)