The reason it has been claimed for years that the speed of light is constant is because this idea supports the deep time required to make Big Bang and Evolution work. Without it it’s less proof that there is evidence for this. So science hid for the longest that they knew the speed of light was not constant and never was.

Reference: New Scientist

Physicists freeze the motion of light for one whole minute.

Reference: phys.org

Speed of light slowed

Reference: BBC News

Speed of light no longer constant

Reference: Live Science

This makes light years wrong, the distant of stars and planets base on the speed of light wrong. Every theory and paper written using this idea that the speed of light is constant wrong.