Let me describe my issue and see if it's the same: I have an ATT modem and router for my fiber connection. I have this connected to my Google Nest WiFi Router. I also have three Nest WiFi Points in a mesh network. I can open the Google home app and it will tell me everything is working just fine!

However, when I try to connect literally any device to the network, it fails. Pixel, laptops, other Google devices, etc.

Is that similar to what you're experiencing?