@cloudwalker it's solved! The solution was in the Dial Up Settings, there I had to change the PDP type. No idea what I did exactly, but it works again

@David-TP Thank you! I have tried to switch the GHz band and channel 11. Both does not work. The error message on Google Home app is clear: no wifi connection

I did a reset to the factory default and after that my chromecast does not connect to the wifi. The TV is connected and my iPhone as well. I have restarted and reset every device. Nothing works. I...