I'd create a State of Nature to preserve the pre-civil culture of northern Europeans -- not just to "save the world" but because that's the enrivonment I want:
1) Buy up large tracts of undeveloped land in nations, in exchange for low land value taxation, that agreed to let people, on those lands, live by the 7 points of agreements between individuals outlined in the aforelinked blog post on "The State of Nature".
2) Permit any indigenous peoples to remain so long as they agreed to those points, excluding everyone else but invitees of the people in those nature preserves. This includes financing a nature preserve patrols (drones, etc.) to prevent encroachment.
3) Set up a cloning foundation to clone people who have been taken out of the gene pool by the current dysgenic culture -- particularly highly intelligent and attractive females that got conned into giving up childbearing for a "career".
4) Set up a foundation for emergency relocation of population when a host nation violates their agreement to permit autonomy.
5) Invite people I like personally to the nature preserve in which I want to live.
6) Invite other lonely billionaires to live in other nature preserves so they could enjoy the natural healthy relationships with beautiful intelligent women.
7) Do what I can to help Bezos, Musk, et al to reduce civilization's ecological footprint on the biosphere -- preferably by space migration. This involves all manner of technology.