After you install "February 27, 2020—KB4535996" Windows Updates the system signing tool (SignTool.exe) no longer works properly.
Therefore when you try to build a setup project configured to be digitally signed, Advanced Installer throws the following error:
ERROR: Digital signature. KB 3118401 is not installed. Selected "signtool.exe" requires the Windows update known as "Update for Universal C Runtime in Windows, KB 3118401"
This is due to a check we perform to determine that SignTool.exe and its dependencies are installed and correctly functioning on current machine. And unfortunately this is no longer the case after applying KB4535996 update.
After this Windows system update it seems SignTool.exe no longer works.
We reported this issue to Microsoft and will be waiting for a fix.
Until Microsoft fixes this bug the only workaround we found so far is to manually rollback/uninstall KB4535996 system update.