Nest + Homey = Dead API by 31th August

It is no longer possible to pair Nest devices with Homey. Only devices added before the 31st of August, when the Nest Partner API was discontinued, will continue functioning. Therefore, this App is deprecated and can no longer receive support. Read more.

From the readme file from the latest update of the Nest app. So only for current users, that’s why the app isn’t in the App Store anymore most likely.