Devices connected to Google Wifi mesh router become unavailable on Home Assistant

Hi. I am new to Home Assistant. I have Google wifi Mesh router at my place connected to ATT Fiber router. The home assistant is installed on a mini-PC that is directly connected to the ATT router via ethernet. Any device that is connected to the ATT fiber router is discoverable by the home assistant. However, as soon as I connect a device to the Google Mesh router wifi, it becomes available. Any thoughts? Appreciate the help.

The two routers use a different IP subnet. The easiest solution, from a network perspective, would be to use the Ethernet port on the Google Master router for your PC.

Thank you. I will try it. However, I am worried that this might make all the devices that are connected to the ATT router unavailable.

Any device placed on the WAN side of a router is considered external.
If HA is placed on the WAN side, then that router needs to be configured for that traffic.Some devices use protocols that can be handled with a portforward on the router, but many discovery protocols require special setups that not all routers make available for users.