"Dark energy" is a hoax, an invention, I would even say, a scam. It tries to get you look away from the truth.
The invention of dark energy is related to the incapacity to understand that cosmological redshift is not an expression of the expansion of the universe, but mainly caused by the interaction of light with matter (hydrogen) in the universe.
It has been observed that the later that light arrives from a sudden cosmic event (like Supernova explosion SN 1987A), the more redshifted it is.
That means that the interaction with cosmic hydrogen delays a bit the light, and takes some energy away from it at the same time.
The neutrinos arrived sooner than the first light.
So, nothing to do with an alleged Doppler effect.
It is a disgrace how the mainstream continues to support fallacies like an "expanding universe", which even creates the need to invent a totally meaningless and mystical "dark energy".