You could house every human on the planet in their own typically English-sized house, place all those houses side-by-side, and it would all fit inside Texas.

Overpopulation is a deflective racist ideal in the context of trying to tackle climate change.

Some areas of the world are very densely populated, true. Those dense populations sometimes live under conditions that are poor for the environment.

"Overpopulation" implies people are a surplus, rather than focusing on the poor distribution of wealth or resources between them.

The world could easily sustain the human population it currently has. The population isn't over any sort of capacity. Rather, the systems that govern them are, and the means to live sustainably are denied to the majority, by a minority who hoard wealth and resources.