At some point in my trying to diagnose the issue I ended up at https://us.flow.microsoft.com/en-us/. There I was able to create a new flow and edit it after the initial creation. Of course now I have 2 separate "accounts" in Flow though they are with the same login username/password.
Are GCC tenants still being rolled out Flow? It has appeared in my tenant for about a month now so I'm unclear why the basic functionality isn't working properly.