FYI, fire alarms are designed to become more sensitive as they age/die so if yours is picking up false positives, it’s a good indicator you need to replace it. That, or it really is poor ventilation.
But to the credit of Nest/Google/Alphabet they replaced it free of charge. It was just an off-the-cuff comment I made on Twitter and Nest said send it back. They sent a new one, a new model, and when it arrived I sent back the older model. The new model is much better essentially zero false positives due to water vapour.