You appear to have submitted multiple support requests concerning the same issue. I’ve merged them into your original post - to expedite troubleshooting, please respond only on this thread instead of creating new threads through the intake form.
The Eero router you’ve mentioned is a mesh-based model. Are you relying on a WiFi connection for the device with which you’re having issues connecting, or are you unable to access RoonServer on the main Mac in your setup?
Please share a screenshot of the page indicated the connection error. If a “Select a different Roon Server” option is available, what happens if you click there?