Overpopulation is a big problem, I agree. (So are declining birth rates in a lot of developed countries (alongside ever-increasing life expectancy). Bit of a paradox. That needs fixing or it may cause big socioeconomic problems down the line. Combine that with automation and AI and it accelerates it. You can replace a lot of the young workforce with robots, but you can't replace them as consumers (yet?), so who's going to buy stuff in a consumer economy (or support the unemployed young people if their jobs get automated and they don't have the opportunity to upskill? Robots can't pay taxes or contribute to your pension fund either.)
If you're talking about how the narrative shifted from the 80s/90s when everyone talked about environmental problems like global warming, deforestation, desertification, acid rain, pollution, recycling, hole in the ozone layer, species going extinct, oil spills, landfill, etc, and then it somehow all got smooshed together into "climate change" as the One Big Problem, then I also agree. Big own goal by the environmental movement. People can just dismiss that and throw the baby out with the toxic bathwater and we carry on as normal and forget about the other stuff.
Seems you hardly ever hear about deforestation these days. Bit harder to argue with that. Can just look at photos of the Amazon. I'm not sure trees are falling down by themselves. Unlike with climate which is super complex, takes ages for the full effects to show themselves, and we can debate it til forever (or at least til one viewpoint is proved right).
Thing is, though, if humans aren't having any impact on the climate by burning fossil fuels, then surely it shouldn't make a difference to the climate anyway whether we have 9 billion people or 50 billion producing CO2? 🤔
I think you're maybe talking about the other environmental stuff which is more obvious. Nine billion people make a lot of pollution and plastic waste and put strain on natural and other resources like water, food and land. That's still a problem even if we don't accept that humans are causing the climate to change. I think we've all got a bit distracted arguing over climate and have forgotten some of the other problems.
Even if we can't agree on climate change, I think we should still be all hands on deck to fix the other stuff. You can probably already notice the difference in wildlife in your own garden/neighbourhood from 20 years ago, and how many birds you hardly see any more. My 2c.