on my 2012 Macbook pro “Dwarf Ethernet” shows up in the list (I previously had it connected to the macbook) but it reports that the device is not responding
Yes in terminal. It is needed to help diagnosing the problem.
It will try to reach the dwarf from its name or for its address.
If the address works and the name not it is a DNS issue
If also the name works it is a browser issue
If also the address fail it is a low level network issue. You could try to manually specify the IP for that port to check if it is a DHCP issue.
Otherwise it could be a driver problem or a dwarf setting problem, this is why I asked to try to connect to a different PC, possibly non apple and to verify the USB setting of the dwarf