There is no such a thing as a fossil fuel
Complex, but best solution. Do a proof of concept of a city built and operated solely on alternative energy. That means NOTHING will contain fossil fuels, from plastic to furniture to medical equipment, to construction material. First occupants will be the UN. I suggest Sinai as the location, since there is a water source for desalination and year round sunshine for an endless supply of solar power.
Every company around the world can work on the project to test their technology. Based on their successes, the technology can be integrated into projects anywhere on the planet. There will be no political agenda.
As subprojects are completed, people who are working on projects can move their families there. Farmers can start to build greenhouses. Scientists can begin baselining local climate and weather patterns. STEM programs to support new technology developed for the new generation of students who will be the guardians of our future.
That’s the way this will work.