Not all is right yet with the transition to the new ARM-architecture Macs. In particular, my MBA seems not to want to install numpy using pip. To get to that point, however, I did the following:

Set the shell to the preferred architecture:

arch -x86_64 /usr/local/bin/zsh

Set my preferred shell:

/bin/bash

It looks like the architecture is correct.

$ bash --version
GNU bash, version 3.2.57(1)-release (arm64-apple-darwin20)

I may try re-install MacPorts and then Python and PIP from scratch, in the hopes that 6 weeks after I first did the above, things have changed and are less wonky.