Thanks for the info, this really helps.
If you unplug the PC Ethernet cable from the Panoramic WiFi Gateway.........we'll call it the "gateway".......and connect a 5-port Ethernet switch to the gateway then the PC can connect to the switch and so too can the Time Capsule connect to the switch.
In effect, your gateway will now have 4 Ethernet ports for devices to connect instead of one.
In addition to the switch, you will need 2 Ethernet cables.....one to connect the switch to the gateway and the other to connect the Time Capsule to the switch. You will still have 2 additional open Ethernet ports on the switch to connect other devices in the future if needed.
Because the Time Capsule will be connected to the gateway network, you will be able to back up the MacBook to the Time Capsule over the gateway WiFi network.
The Ethernet switch will not affect the speeds on the network, it will be totally transparent. An example of a recommended switch would be something like this:
https://www.amazon.com/Ethernet-Splitter-Optimization-Unmanaged-TL-SG105/dp/B00A128S24/ref=sr_1_4?dchild=1&keywords=5+port+ethernet+switch&qid=1592158000&sr=8-4
So, the Time Capsule does not need to be connected to WiFi, it needs to be connected to an Ethernet port on the switch.
If this sounds like it might make sense and you are up for resetting and reconfiguring the Time Capsule, post back for more details. In addition to an Ethernet switch, you will need 2 more Ethernet cables......any length or color that you want.
If you want to go to a store to get the items, any big box electronics retailer like Best Buy or Frys will have what you need.