I have always noticed it spiking while cooking, but never worried about it because it wasn't sustained.
I already worry about enough things, so I have to draw the line somewhere I guess.
The biggest thing is, if you have good air quality outside, you need to keep your windows open as much as you can. I'm using sensors on all the windows at my place, and a temperature sensor outside and HomeAssistant, which tells me when outdoor temperature is lower than indoor, so I know when I can open the windows and not use additional HVAC capacity. That keeps indoor air quality in-check.
If you live somewhere with poor outdoor air quality, you likely need a filter to clean your air up at least a little. That can be a standalone air purifier, or it could be as simple as a HVAC filter taped to a cheap box fan. Keep your filters changed every few months, never have to dust again, and enjoy cleaner air. Simple.
Generally, any HVAC system will dry the air quite a bit, but only when it's running, so if you live in, say, Kentucky, it's likely that if outdoor temp = indoor temp at night, you can have your windows open, and when you close them in the morning, the next day's worth of HVAC usage will take care of any additional humidity without much trouble.
The real downside of that is that you'll have to run your HVAC system harder, because dry air feels cooler than humid air.
Unclear how much is due to the combustion of gas vs. also the cooking of food, as others have mentioned. I suspect it’s almost entirely from combustion of the gas. Though, I have noticed that the CO2 levels don’t climb as high if simply boiling water on high heat.
Depends who “you” are, just as for outdoor air quality.