Degrowth is false. If we lost population, the environment would get worse - as we wouldn't be able to maintain modern technology, we'd go back to the real bad stuff like coal and wood burning.
The US's total CO2 emissions have been going down for a decade or two now, even after population growth. And no, it's not because we outsourced them.
But I don't trust humans to make such collective sacrifices willingly. We're just too lazy, stupid, and selfish.
I think the more likely outcome is that reality will control our population for us, via drought, famine, war, and epidemic.