After some research I have found a fix. Doing this bypasses MacOS security so only do this for applications you can trust
I downloaded a fresh copy of EDCE for Mac (just in case) and extracted the app from the zip file. I moved this app to the /Applications directory.
Then in Terminal I typed the following command line
chmod +x /Applications/EmpireCombined.app/Contents/MacOS/EmpireCombined
Following this the icon in /Applications is double clickable but will not run because the developer is unknown.
Click cancel in that dialog and immediately open Preferences.
Open Security and Privacy and navigate to the General tab, in the lower part of the window there will be a remark about the developer of Empire Combined being unknown.
Click "Open anyway" then click open in the resulting dialog box and you should now be in business.