Hello davidmarcus,

We understand your Google Chromecast says “No devices found “ lets try changing the security mode . Let me guide you the steps on the same .

Please login on the web manager (192.168.0.1) 

Launch a web browser, such as Internet Explorer, Firefox, or Safari.  Enter http://192.168.0.1 into the address box, and press the Enter key.  The https:// Redirect page will appear.  
The SURFboard Web Manager is begin redirected to a more secure connection, click the Proceed button to continue.   

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NOTE: A security or private risk alert may appear on the web browser advising users to proceed with caution when accessing the Web Manager.  There is no risk in proceeding to the Web Manager.  For instructions to bypass the alert screen, refer to article # 18181 - Alert Message for Web Manager Access.

Once you are on the gateway page . please select Connection <> Wi-Fi <> towards right side you will see the Primary Home Wi-Fi Network « select 2.4 Ghz select WPAWPA2-PSK(TKIP/AES) and save the changes . Also please repeat the same with 5 Ghz.

Do let us know if this helps. 

It is Chrome on the desktop computer that can’t find the Chromecast. Both the Chromecast and the desktop computer are connected via Ethernet to the SURFboard. So, it seems unlikely that changing the Wi-Fi settings will help. But, SURFboard support suggested trying Wi-Fi for the connection to the Chromecast, so I will try that this weekend.

I have only 5Ghz enabled, and it is set to WPA2/WPA3 Mixed Personal (AES).

I connected the Chromecast to the WiFi. Now, other devices on the WiFi can detect the Chromecast and cast, but devices on the Ethernet cannot.

I also tried connecting the Chromecast and my desktop computer to a TP-Link Ethernet switch. Sometimes the computer could detect the Chromecast, but sometimes it could not. There did not seem to be a pattern.

So, I'm going to leave the Chromecast connected to the WiFi.