@cameogt 

Hi,
1. The Tapo cameras do not have the feature to switch the Wi-Fi network automatically when the connected Wi-Fi network has no internet connection. In your situation, if the modem supports internet source backup, such as when the internet cable goes into the modem does not have an internet connection, the modem can switch to a backup internet source(e.g., 4G or 5G SIM card), so the client devices connected to the modem will continue to work.

2. In this FAQ(How to connect Tapo Wi-Fi Cameras/doorbells with Tapo Hub), the Tapo H200 and the camera should be on the same network, such as connected to the same modem, then you can use the Wi-Fi backup feature. This is different from the scenario you want.
 

Best Regards