“started trapping all their Carbon Dioxide”
One problem with this speculation by the scientists that loss of CO2 caused it, is that the Martian atmosphere is still 95% CO2. So if Mars was losing CO2, it apparently wasn’t losing it any faster than it was losing the rest of its atmosphere.
If you look at Mars’ atmospheric composition, it looks pretty much like a solar-wind stripped result if you started with an atmosphere similar to Earth’s.
The CO2 is essentially the heaviest gas in the mix. Some of the oxygen and most of the carbon available early on would have stayed CO2 since there is no plant life to decompose it and store the carbon. The argon is the product of potassium beta decay and is stripped by the solar wind, keeping it in an equilibrium or at least present. And the oxygen and nitrogen are the remnant that still have not been completely stripped by the solar wind, even the ratio is reasonable given that nitrogen is a bit lighter than oxygen. And water vapor is even less dense than either, so it would be gone as well. So, it is not a wildly fantastic claim that the current Mars atmosphere is the solar wind ravaged dregs of a once-Earthlike atmosphere.
In a different post you claim that Mars has no magnetic field so it should have lost its atmosphere much faster than it apparently did. That would be a valid argument if Mars had never possessed a magnetic field, however, it almost certainly did possess one early on given the amount of iron present. Thus the loss of atmosphere would have begun slowly and accelerated as the magnetic field dissipated once the cooling of the planet progressed. And Mars, being much smaller than the Earth, would have cooled considerably faster than Earth, so it is not at all peculiar that Earth still has an atmosphere while Mars does not. Given enough time, we will look like Mars in terms of dryness and thinness of the atmosphere.