Catalytic converters have to convert a tiny part of the output, and they convert them into more stable forms.

The problem with CO2 is that it's the most stable form.

Also, if you want to absorb the CO2, for 1 pound of fuel you get like 3 pounds of CO2. You can absorb it into a solid and the density is like 3 times the density of the fuel. So with a lot of approximations you need container that has the same volume than the fuel tank to store the CO2, or even bigger if you absorb it in a liquid or much much much bigger as a gas. And you must empty/exchange the container when you refuel. And then you realize that it's better to use an electric car.

If we were serious about CO2 capture, then the place to start would be big producers (like coal plants): Because that way you need much less scrubbing efficiency and can tolerate much greater overhead while still being effective.

If a technology is not good enough for at least serious trials in that (much simpler and more forgiving) usecase, then there is no point in discussing it for small environmental air scrubbing. That is akin to talking about electrifying passenger planes before having a single electric vehicle on roads.