Correct, but that shows what an chemical engineering masterpiece photosynthesis is.

It also isn’t just one step, but multiple smaller steps in between, which make it possible to break the C-O bond.

But the difference is, that for photosynthesis, there are other reaction partners that are able to bond to the Carbon and Oxygen atom. For the decomposition, they likely were in a pure CO2 atmosphere, making it hard for the atoms to find better reaction partners than each other.