Could potentially explain the "negative gravity-like" force causing the universe to accelerate in its expansion. Can't rule out anything too quickly.
I suggest reading up on Vera Rubin. The 4% Universe is a good start.
Dr Rubin showed that there is definitely an effect there.
The cause is still in question, but, it is known that gravity without pressure will act as a repellent force. This is basically the effect Einstein’s Cosmic Constant is there for. He didn’t like that part of the equation.
Or maybe the universe isn’t expanding, and redshift can have causes other than relative velocity. Really, it’s hard to express how far from genuine science one needs to get in order to assume “negative mass” can be a thing.
It breaks the very semantics of the word “mass” to attach “negative” to it. Mass is either zero (does not exist) or positive (does exist in some amount). Try to think of holding in your hand negative grains of sand. What would even qualify?
This is religious behavior - “save the gravity-driven view of the universe at all costs” - and not scientific behavior at all.