Catalina

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

I am aware of two possible solutions (though can't confirm either, as I have no intention of installing Catalina until it's fixed).

All workflows at once

@baa76 suggests that adding Alfred to "Developer Tools" will stop Catalina griping about unsigned binaries:

Individual workflows

Apparently 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.

Alternative method

@jefftriplett posted a solution here:

1. System Preferences >> Security & Privacy >> General
2. Click the 🔒 to allow changes
3. Then check out the Allow apps downloaded from: [x] App Store and identified developers
4. Restart Alfred
5. Try the workflow again
6. Back out of Security & Privacy
7. Re-enter Security & Privacy
8. There should now be an Allow <binary-name> option which you'll want to allow
9. Restart Alfred again
10. Try the workflow again and repeat the steps 6+ as needed.