[m46ah_30]

That did it. I knew from Classic that there was a difference between the alias and the identity and that creating an alias did not automatically create the idnetity. What confused me was the inclusion of "fetch from" in the identities. Did not want to fetch from... I wanted to send from! But I created one anyway for the missing alias and it now appears where I expect it to be in the composing screen "From" dropdown.