When you install a Nest Learning Thermostat in the Google Nest app, it should AUTOMATICALLY appear in the Google Home app without any action on your part.
However, in recent months, customers this forum have been reporting this isn't happening. Many customers have done the following to make it work: In the Google Nest app, create a temporary second Google Nest "home/structure". Then, in the Google Home app, go to that empty temporary Google Nest "home/structure" and delete it. These steps seem to force the 2 apps to sync and causes the thermostat appear in the Google Home app.
Another thing to check is whether your thermostat is assigned to a "room" in the Google Nest app. If it is not, assigning it to a "room" in the Google Nest app then causes it to appear in the Google Home app.
This worked perfectly for me... another factor that wasn't helping in my case was being part of multiple homes, but leaving the one I didn't want to associate nest with, and then following your above instructions worked a dream. Merry Christmas and thank you!
I am having the same problem. I updated my router and reset the Gen 3 thermostat as I was supposed to then deleted it from my account. When I open my Nest app I click login with Google and it is a forever loading loop after allowing access to my account. I CAN access my account via website but I cannot add the product to my home or use the Android App at all.
Prior to the create a new home structure reply, I found that elsewhere and did that and was successfully able to add it back into my home. After I was able to log in with the Nest App. Everything on the Google Home app worked fine, it was specifically logging into Google through the Nest App which is the only way I could add it to be controlled by Home.