We have run DeveExpress Project Converter in Visual Studio to upgrade our clickonce from 17.1.5 to 18.1.3. Problem was that after the conversion 2 dlls, DevExpress.Images and DevExpress.RichEdit.Export were added to the Application Files (Publish tab) list with Publish Status as PreRequisites. The impact of this is that deploying the app showed an error message stating dll ***** was required to exist in the Windows GAC folder.
The solution, therefore, was to change the Publish Status of these PreRequisite dlls (in our case, to Exclude, because we deploy all devexpress from an external zip, in an external process - but usually you will set this to Include).
After that, publishing will generate a manifest that does not show these dlls with PreRequisite dependencies, and hence you are rid of the deployment installation GAC message.