The problem in this discussion is that you don't have an understanding of the concepts involved. You haven't properly understood the LIGO experiments and you clearly know nothing of general relativity. There really is no point in continuing this further.
It doesn't looks like you wanted to discuss flaws in GR with a dissident, who, obviously, too stupid to understand GR and SR. You told me that. You did the job. Now, «shut up and calculate».
You started this discussion saying "LIGO, VIRGO, and NANOGrav experiments and observations proved that speed of light in vacuum is NOT constant".
This is completely absurd, as anyone who works in the field will tell you.
I never said you're too stupid to understand. What I said, and maintain, is that you lack a basic understanding of the concepts involved. If you want to have a proper discussion, you need to first properly study general relativity, and refrain from making ridiculous assertions about things you are obviously not an expert on.
If we want to predict what the camera attached to a rocket moving along a complex trajectory at a speed close to the speed of light will see, we need a powerful theory that can predict the image and characteristics of other physical processes that this camera will observe. The Theory of Relativity and the Special Theory of Relativity can predict these characteristics. However, the Theory of Relativity doesn't explain the «why» behind this happening.
If we consider the theory of the ether, the speed of light is the speed of wave propagation in the medium, which is itself determined by the speed of an interaction between particles in this medium (which is usually higher than the speed of wave itself).
In the case of experiments like LIGO/Virgo or NANOgrav, the speed of light changes because gravitational waves affect the medium.
If we take General Relativity (GR), the speed of light is the ultimate speed because Einstein stated so.
In the case of LIGO/Virgo experiments, the speed of light remains constant because the speed of light is the constant, as stated by Einstein, and space and time stretch in the 5th, 6th, 7th, and 8th dimensions, which leads to light moving slower, although the speed of light itself doesn't change. :-/
