The tado° app needs to work in the background if you are using Geofencing on tado°.
To make sure that background data is activated in the Android settings, you can follow this simple guide provided by Google.
If you experience any issues, please also verify that the background data refresh is not being restricted by any battery optimizing settings.
More information:
How can I turn off the battery optimization for the tado° app in Android on Samsung devices?
How can I remove the battery optimization for the tado° app in Android on Huawei devices?