Couple points here about added CO2 as a "fertilizer" for plants.
Yes, added CO2
ceteris paribus would be a good fertilizer for plants. BUT added CO2 will (and already is) affect the climate. Meaning that a local climate may become DRIER overall due to changing precipitation patterns. Or it may become WETTER. Not all plants thrive under drier or wetter conditions uniformly. Just ask any gardner.
The myth of added CO2 being a net benefit is a gross oversimplification and requires that literally nothing else change. Unfortunately that isn't how any of this works.
You don't have to believe me. You can read this:
The familiar adage - too much of a good thing is a bad thing - applies to atmospheric carbon dioxide: In higher concentrations, it is a damaging pollutant.
yaleclimateconnections.org