Hmm; that should work. Is there anything interesting in the verbose log?
Also, maybe it’s worth checking your $EDITOR? It should block and wait for you to save & close the text file. If it’s opening a GUI editor, it may be returning immediately instead of waiting. Many text editors have a CLI option to make it wait so it’s more suitable for use as $EDITOR.
I changed the default editor to nano and it worked without a hitch. Is there a way to change this setting within beets? The docs mention environment variables, but not how to change them.
Environment variables are not a beets thing; they’re an OS thing. You’ll want to google for advice about how to set environment variables on your platform.