I assume you mean “CO” detector. CO2 is Carbon Dioxide and I don’t think you went out and purchased and installed a detector for that.

High humidity levels can absolutely cause a false alarm on a CO detector. Example: safeinhomeair.com/carbon-monoxide-humidity/

I’ll also point out that not all CO detectors are created equal. There was a lot of news about this earlier this year where a number of CO detectors sold on Amazon simply did not work, or did not meet published safety and detection standards. Here’s an example of some of the serious warnings that were published: cpsc.gov/…/CPSC-Warns-Consumers-to-Immediately-St… . Following that announcement, there were several other brands and models that were flagged as being non-compliant. If you haven’t done so already, find your make/model and verify that it’s not one of the sub-standard units that were pawned on Amazon for years.

CO detectors also need to be replaced (they don’t last forever). Most use chemistry to detect CO levels, and that chemistry begins degrading as soon as the unit is built. Some last just a couple years, some are designed to last up to 10 years, but the point is - they all go bad eventually. How old is your detector?