There are too many humans on earth.

Grand strategy solution:

Somehow a lot of humans have to be taken out of poverty and also be educated as that leads to them to having fewer children and healthier, more productive lives. This would slowly decrease the population ( as seen in more developed countries ) on earth.

Technology has to be researched that can care for and keep the majority of older age population productive and healthier for longer as the younger population become a minority. A healthy longevity for all.

People should be able to live free, the way they want, in their preferred culture and political system of choice. There should be a way to end all wars with less people having to compete for land or resources.

Most of earth would be left for nature to populate, with us there researching and learning more about our world of course. Most humans living in huge high tech cities ( mega cities ) that produces no non-recyclable waste and food grown indoors ( vertical farming, aqua farming and others). There should be smaller societies outside of these huge cities, these smaller societies more or less blending into nature, preserving older techniques of farming including hunting and fishing, living for those who prefer that kind of life. Including those primitive tribes that have little or no contact with our civilization.

Energy should come from fusion and other environmentally friendly sources.

With a highly educated population on earth we can find ways to spread our species and life itself to the neighboring stars. Earth's existence is finite.