I have a Nest Learning Thermostat 2 gen that I use to control a humidifier as well and I noticed that the humidity setting levels have no option for an automatic mode and they do not change with outside temperature. This is a big problem where I live as temps routinely drop below zero in the winter and with the nest keeping RH levels high I wind up with major condensation issues if I don't constantly monitor the setting.
I saw on @tanderson097 's post, https://www.googlenestcommunity.com/t5/Nest-Thermostats/Nest-Humidity-Control-RH/m-p/39578/highlight... that they had similar issues but that the original humidity setting also didn't include numbers but only droplets. I noticed that shortly after I enabled humidity control on our Nest that the setting went from droplets only to an actual RH level so I assumed the update to change settings based on outside temp had also been pushed but it has not.
Please enable an automatic control ASAP, this can cause severe damage to a house and I don't think many people would assume that a Nest thermostat is only capable of manual humidity control. I know they lack a true outside temp sensor but being internet enabled the local forecast should be plenty accurate enough.
This is a long term shortfall for the Nest thermostat. It used to have APIs allowed that gave access to programmers, and a guy in Canada designed a system for varying humidity with temperature. Any Nest user could setup their personal Nest on their server, edit the parameters, and it would control humidity. When Google bought Nest, they disabled those APIs which ended that setup.
Google has not responded to this request to build a humidity control varying with temperature for years now. It would be great if they would, as water condensing on windowsills in freezing temperatures is indeed damaging and causes mold growth too.