I just think the neutrality, reduction in resource use and sustainability has to come first. Otherwise Jevons. Of course there can be intelligent overlap. I would hope that as nations move near to neutrality they must have put effort into a rethink of agriculture and forestry (and every other human activity).
Now they can re-plant locally appropriate species and create new forest that will eventually appear to be entirely natural ancient woodland or rain forest. Forest that's destined to be mainly left alone as carbon sequestration. Along with wood production that's sympathetic to the planet and sustainable.
Greening deserts feels, to me, like a "near neutrality" re-wilding project. Something we can think of adding in a push to carbon negative, to undo some of the damage done. Something to do after we have sustainable, renewable electricity everywhere network to desalinate and irrigate. Something that can be carefully seeded to take account of species and that appears and acts natural, and stays put as national park or reservation. Without destroying yet another wilderness.
Not as a green project slapped down as Deus ex machina solution in a world that's not yet moving to neutrality. That risks making it worse. In fact it will almost certainly make it worse as coal and oil is still permitted to keep on looking for new markets and uses.