Hello @Josemhrosa
The Nest WiFi Pro units use the 6GHz band for their mesh interconnect (along with supporting 6GHz WiFi clients), unlike the earlier Nest WiFi and Google WiFi products, which used the 5GHz band in a similar way. 6GHz is theoretically capable of much higher speeds – however, the FCC regulations require using a lower transmit power in that band unless the equipment supports an automatic frequency coordination feature that would collect equipment location and submit a request to a cloud-hosted service to request permission to transmit at the higher power in that location. This avoid interference with licensed users in that band (things like weather radar). Google has not yet announced the availability of this feature, so Nest WiFi Pro transmits at the lower power in the 6GHz band. This requires placing secondary/point units closer to the primary in order to get the ideal "great" result from a mesh test.
You asked whether you could connect one of those weakly-connected secondaries to a nearby Ethernet connection that is part of your service provider network. The short answer is "no" – the primary/router Nest WiFi Pro unit is creating a new "inner" network, and all of the secondary/point Nest WiFi Pro units need to be connected to that "inner" network, either via the wireless mesh connection, or via Ethernet into the LAN Ethernet port on the Nest WiFi Pro unit. They cannot be connected via Ethernet to the "outer" network (the one the primary Nest WiFi Pro unit's WAN Ethernet port is connected to).
So, the long answer is, you are on the right track with thinking about connecting it via Ethernet. You just need to connect it to the LAN port on the primary unit, either directly or through an inexpensive unmanaged Ethernet switch. If you can't arrange that easily, you may also be able to build an "inner" wired network using coaxial cabling and MoCa adapters. Just be cautious to use proper filters to ensure you don't expose that network to other apartments (for example – if you're in an apartment building).
If neither of those options are available, try moving that weakly-connected secondary closer to the primary. One or two rooms away, at most (and for 6GHz, one room is best). From there, it will provide access to more distant client devices in the 2.4GHz and 5GHz bands (and nearby clients in the 6GHz band).
I hope this helps!
