Hi, welcome. TTS is meant to talk to people around the nest device. It seems like you are expecting the Nest to listen as well and execute what it is saying? That is not what it is supposed to do. It is just a spoken message, not a voice command. Unless you yourself are willing to do what the Nest tells you to.
Nabu Casa Cloud provides a text to speech engine to convert text to sproken words, and it integrates your devices is Google home so you can tell it to do things. But these two are separate things.
I believe there are integrations to execute commands on the nest, but these integrations do so without speaking.
Hi, thank you very much for your reply
As an example: an automation is running and the Google Nest device should tell me that (as an example: the laundry is done)
I can address the device with “call service”, but then I don’t get any text output
exactly that
I test that it works with the “browser” option
If I enter a cast device as the target, the cast device is activated but does not output any language