People talk most about CO2 because it has the most total effect as a driver of climate change. CH4 for example has a greater effect per kilogram, but we emit a lot less of it and it doesn't last nearly as long.

H2O technically affects the temperature even more than CO2 but it's not a driver, because the total H2O in the atmosphere depends on overall temperature. Emitting more H2O, from hydrogen cars or something, would just mean you get more rain somewhere.

Yeah because it’s the biggest new contributor. Technically water is the biggest green house gas but there are good reasons for focusing on CO2.

Yes and:

And it's very likely any fixes will not simply be a matter of reducing atmospheric carbon.

Here's a first principles explanation for why carbon net zero and sequestration are not the direct, most expedient path towards reducing temps.

"Dr. Ye Tao on a grand scheme to cool the Earth" https://www.volts.wtf/p/volts-podcast-dr-ye-tao-on-a-grand#d...

TLDR: Given the time and resources we have, focus on strategies for cooling the atmosphere the fastest way possible.