@MauryG5
Just a shot in the dark here.
Your Mac has one ETHERNET port and one wifi port. Yes?
and Debian uses the wired ETHERNET port.(?)
How many inputs does your router have for you to use?
If you only have one input available then I suggest you get a ETHERNET switch.
You can then plug several devices into the switch and plug the switch into your router. The modem should see all the devices on the switch and assign each a different IP address. Once you have the address of the BB then your Mac/Debian can talk directly to the BB through the switch.
This is the switch I use.
https://www.trendnet.com/products/unmanaged-switch/8-port-gigabit-greennet-switch-TEG-S80g-v4Be sure to unplug that BB port when you finish or block that ports mac number in the router so it does not connect to the internet.