For some time there’s been a problem between Gnupg 2.4.1 and Emacs. Although you can decrypt files with Emacs—your .authinfo.gpg file for example—you couldn’t edit and save an encrypted file: Emacs hangs. This turns out to be a mismatch between the way Emacs and Gnupg expect to communicate the password and apparently it’s a hard problem to resolve. Until one or both apps are fixed you need a workaround.
The workaround is simple: downgrade to Gnupg 2.4.0. That’s not hard, of course, if you compile Gnupg yourself, but is harder if you use Brew to install it. There’s no easy way to do that with the standard Brew commands and the process that I’ve seen previously seemed a bit complex.
Álvaro Ramírez to the rescue. He has a post that gives us a simple procedure for doing the downgrade. Basically, you just download the Brew recipe and then install it using standard Brew commands. I’ve already done that and it took me less than a minute so there’s no reason not to follow his prescription if you’re having the problem.