Do the following immediately after you get the warning: "[application-xyz] cannot be opened because the developer cannot be verified."
1. Click "Cancel" on the warning dialog.
2. Open Mac System Preferences
3. Open Security & Privacy section, then the General tab
4. At the bottom in the "Allow apps downloaded from" section, you should see a message that says: "[application-xyz] was blocked from use because it is not from an identified developer."
5. Click the "Allow Anyway" button
6. Try to run the workflow again
7. You will get another warning about not being able to identify the developer, but now it has an Open button. Click Open.
8. You show now be able to run the workflow without any future problems (until you upgrade the workflow).
Apple has more about this work-around at the bottom of this article:
https://support.apple.com/en-us/HT202491
emel got a reaction from Richard Kaplan in Workflow fail with "developer cannot be verified" errors in Catalina