If your window shade absorbs 99.9% of all incoming light, will two window shades absorb 199.98% of incoming light?
If you believe that, then you are ready to become a climate scientist. LW absorption in CO2 bands has been almost saturated since 20 PPM. Adding more CO2 doesn’t affect the energy balance very much, because there is little LW in those bands which isn’t already absorbed.
CO2 molecules can’t capture non-existent photons.