I think it confuses causation and correlation by claiming that having more people, faster population growth, leads to finding solutions to major problems humanity deals with faster. I don’t buy that. In fact, I’d say our inventiveness has been the _cause_ of both population decline and solving the major issues the article mentions (like progressing agriculture to use less resources)
I also think it takes a too anthropocentric stance. In the beginning of the article it claims that population decline is bad for the planet, but surely humanity going extinct does not have a net negative effect on the planet. As many climate change critics are prone to point out, nature will do what it wants despite the influence of humans and nature will adapt with or without us.