Problem Sorted! I didn't need any Post Build event code after all.
My EV Code Signing Certificate was physically delivered to me from Sectigo on a USB Token, and it can only be installed from this token (it can't be copied). I also received a download email with a password, and a URL to download and install SafeNet.
When I'm publishing Jazz, the procedure is: -
Plug in the USB Token
SafeNet was running
Have the password ready to paste
Open the project,
`Signing Tab. Click [Select from Store]. My Sectigo Certificate was displayed, select that.
Publish tab: Click Publish Wizard or Publish Now
Publishing then runs. Several times I was asked for the certificate password, which I gave by pasting
When publishing was complete I copied the application to the my web site and tested the download. Everything worked perfectly, without any appearance of "Windows has protected your PC"