TLDR: 1st Gen Chromecast, don't use a Google Pixel to set it up, use any other mobile device and the Google Home app. I used an iPad.
This is more of an FYI in case anyone else has this same issue. I have the top of the line, very expensive Google Pixel 6 Pro, and 9 different Nest or Google Home devices. I have all 3 generations of Chromecasts, the older ones I just use to play smart slideshows. Anyway, I bought a used 1st Gen Chromecast for just $15 but it was still setup on the old owner's wifi. So I had to hold the physical button 25 seconds until it reset and entered the original setup mode. It then broadcasts its own SSID GoogleChromecast1234 (different 4 numbers). Following all the correct instructions would not complete the configuration, it would fail and give me this response, "Chromecast found. It needs to be activated before setup".
You would think that it would all work great using my $1000 Google Pixel phone with the Google Home app to setup the Google Chromecast with Google's Nest Wifi Router, but sadly that was not the case. Instead after reading a variety of helpful posts on Reddit (because let's face it, Reddit users like to help and Google would just like to sell you a new device) I decided to try the same setup on my Apple iPad Air. How about that, Google Home app on my iPad worked great! So there you go, Google, I'm disappointed in you, but not to worry, Apple helped me fix your stuff. 😉
