That's not it at all. All parties agreed that Congress passed a law allowing the EPA to regular carbon emissions by setting emission limits on different types of power plants based on the best current technology available for emission reduction. The disagreement is whether that allows the EPA to set emission limits which are impossible to achieve, with the goal of forcing fossil fuel plants to shut down or subsidize renewable sources.
I encourage all the tech people around here to "read the code": https://www.supremecourt.gov/opinions/21pdf/20-1530_n758.pdf