The ones in cars need to be heated up quite a bit in order to work, and you still need reference air. Otherwise, I'm pretty sure that CO2 isn't a problem but rather an indication of a lack of oxygen in the first place, so it technically could work... just not if you're measuring the environment itself.

This is in theory not a problem: getting an oxygen sensor to 700 degrees if it's a tiny spec on a chip is not necessarily hard or would even require a lot of power.

But...oxygen concentration is essentially indepedent of CO2. We measure CO2 at part per million levels, whereas O2 is 20% of the air.

(In that context CO2 is surprisingly toxic given that 1000 ppm can impair mental acuity).

No, it's nonsense to assert that CO2 is due to a lack of oxygen.