Enable GPG Mail on macOS Mojave or newer

On macOS Big Sur and Monterey, GPG Mail should automatically be activated. If that did not work or you are still running macOS Mojave, to enable GPG Mail

1. open Mail > Settings > General > Manage Plug-Ins…
   
2. tick checkbox for GPGMailLoader (In case you see more than one GPGMailLoader, pick the newest one)
   
3. click Apply and Restart Mail

Now activate your Support Plan in Mail > Settings > GPG Mail.