> Capping carbon dioxide emissions at a level that will force a nationwide transition away from the use of coal to generate electricity may be a sensible "solution to the crisis of the day." But it is not plausible that Congress gave the EPA the authority to adopt on its own such a regulatory scheme in Section 111(d). A decision of such magnitude and consequence rests with Congress itself, or an agency acting pursuant to a clear delegation from that representative body.
It seems pretty clear that Congress does have the authority to delegate, but that the Court ruled that Congress didn't intend to do so. This ruling places the ball firmly in Congress's court, it doesn't rule that Congress cannot act.
[0] https://www.supremecourt.gov/opinions/21pdf/20-1530_n758.pdf