Catalina

Catalina refuses to run unsigned binaries by default, which affects workflows written in languages like Go or Swift.

There are a few ways to allow such programs to run.

All workflows at once

Adding Alfred to "Developer Tools" will stop Catalina griping about unsigned workflow binaries. Note: you may not have the "Developer Tools" list if you don't have Xcode installed. (Thanks to @baa76):

Individual workflows

1. Open System Preferences > Security & Privacy > General
2. Click the 🔒 to allow changes
3. Run the workflow in Alfred. When you get the dialog saying the binary cannot be verified, click "Cancel"
4. In System Preferences, you should now see an "Allow <binary-name>" option
5. Click "Allow" and the workflow should now work

Alternative method

The "right-click and open" method for unsigned applications also works with binaries:

1. Right-click on the workflow in Alfred Preferences and choose "Open in Finder"
   
2. In Finder, right-click on the binary and choose "Open":
   
3. Allow the workflow binary to run in the resulting dialog

Note: Finder will probably try to run the binary in Terminal.app and it will throw an error. This is expected.