For me the solution was that my developer account is a dedicated account, and not my general iCloud account that I have on the phone. In Xcode, cmd + , to open prefs, click Accounts, add the account that the device is using in here (for me the personal account had been added in the past but the session had expired). Then after logging in there, I went back to the drop down that shows all the devices which still said no eligible devices. I click that which opened up the window. And for me, I unplugged the phone from the cable a few times, but then on a whim I swapped the usb c in the MacBook from one port to another, and it popped up. After that its just an intuitive setup process; select the device that appeared, trust the computer, restart, unlock the device, and there it is. Thanks to everyone that contributed here for the tips along the way.