I’d be a little worried about
I’d be a little worried about heat build-up with the theft shield in place. It looks like there are some cooling slots in the theft shield, but catalytic converters get very hot while operating so I wonder if the vent holes really allow sufficient air flow. It would be smart to talk to Toyota about warranty impact before installing the theft shield if one’s Prius is still under warranty.
CO2 is not converted to H20 by the the catalytic converter, that would require a nuclear reaction.