I suspect those are only supported if your ISP supports multiple IP addresses. Your Google mesh typically provides DHCP and only one device on your network can perform that function. I suggest adding a small unmanaged switch AFTER your primary Google router and connecting your Macintosh to that. 

The following is directly from Cox:

For modems with four Ethernet ports, only plug devices into Ethernet port one because only one port is active, and additional devices plugged into the other ports will not receive Internet access. Use the access port only for modems with a sticker covering up the extra ports. Do not remove the sticker.

The purpose of it its multiple. 

1. if you have a router that supports wan port aggregation, it can supply greater than 1 gig speeds to a router. 
2. for business class lines, it can connect multiple devices and they have a different public ip address. It allows businesses to have their equipment separate from customers or mixing equipment for security. 

@LoveMyLab is exactly correct. Most consumer modems only support 1 public ip address so only 1 device can be connected. There’s a few that support multiple but they’re rare.