The planetary zero-impact carrying capacity for humanity is somewhere between 500 million and 2 billion, depending if we want (respectively) a first-world meat-inclusive diet or a fully vegan diet.

Carbon emissions aside, we are indeed a plague upon the planet. Thanks to high tech, we have massively blown past our carrying capacity, and risk lowering the non-high-tech-enabled carrying capacity down into the mere tens of millions or even less. Which bodes very badly if we experience a severe civilizational collapse in the next 10-30 years (as is becoming increasingly likely) that makes building and maintaining high tech impossible.