We live in a three story house with our main internet connection coming in at the ground floor level. I have a Google wifi mesh setup with three Google wifi routers, the one on the ground floor being connected by LAN cable to the incoming router of my service provider. So the system works well except for the top floor where the mesh signal is weak. I do not have many options in moving them around to try and get a better signal.
I do have a small switch at the top floor which connects directly by LAN cable to the incoming router, which serves our 2 laptops by cable as we are working from home and needed stable connections (90% of our work involves connection to remote servers). It has some spare ports which I am not using.
Can I connect my Google mesh router at the top floor directly to my switch in order to enhance the wifi signal on this floor?
I am not an IT fundi so excuse the non-technical language.
The Google WiFi unit on your ground floor is the primary. It is connected to the "outer" network created by your incoming router, and then it creates a new "inner" network for your WiFi clients. But, that "inner" network is also available through the "LAN" Ethernet port on that primary Google WiFi unit.
With all of that as context, you can connect a remote/secondary Google WiFi unit via Ethernet, but it has to be connected to the "inner" network – not to the same "outer" network that the primary Google WiFi unit is connected to.
So, if you can arrange to have that Ethernet cable connect to the LAN port on the primary Google WiFi unit instead of to the "outer" network, then you can connect one or more of those remote secondary Google WiFi units to that switch to use Ethernet as the interconnect, which should improve performance significantly.
But, it is important to note that when you do this, all of the other wired devices connected to that switch will now be connected to the inner network as well. That isn't normally a problem – they may need to be rebooted, for example. But, they will be on a different network than they were before, so they may no longer have easy access to anything else still connected to that outer network. However, in general, it's better to have everything (wired and wireless) be on the same network as each other, so it may be an improvement.
I also live in a large three story house. However our internet connection comes in at the top floor. It seems to work great and I actually only need one point at mid level. It might be worth switching things around and seeing if originating it at the top would help things out. You could put the router on the top floor connected via cable to your modem, since you have one ran already, and see if it makes a difference.