@atripp But there is no -Source Argument for Publish-Module.

It seems that something want's to go over the company proxy. But my ProGet server is on-prem. Any ideas?

AUSFÜHRLICH: finished running C:\Program Files\dotnet\dotnet.exe with exit code 1
Publish-PSArtifactUtility : Failed to generate the compressed file for module 'C:\Program Files\dotnet\dotnet.exe failed to pack: error Microsoft (R)-Build-Engine, Version 15.9.20+g88f5fadfbe für .NET Core
Copyright (C) Microsoft Corporation. Alle Rechte vorbehalten.
  Pakete für "C:\Users\<user>\AppData\Local\Temp\81f14a76-9d0f-4140-a2bd-a2c2f86a4427\Temp.csproj" werden wiederhergestellt...
C:\Program Files\dotnet\sdk\2.1.505\NuGet.targets(114,5): error : Der Dienstindex für die Quelle "https://api.nuget.org/v3/index.json" konnte nicht geladen werden. [C:\Users\<user>\AppData\Local\Temp\81f14a76-9d0f-4140-a2bd-a2c2f86a4427\Temp.csproj]
C:\Program Files\dotnet\sdk\2.1.505\NuGet.targets(114,5): error :   Response status code does not indicate success: 407 (AuthenticationRequired-kurz). [C:\Users\<user>\AppData\Local\Temp\81f14a76-9d0f-4140-a2bd-a2c2f86a4427\Temp.csproj]
'.
In C:\Program Files\WindowsPowerShell\Modules\PowerShellGet\2.2.4.1\PSModule.psm1:10988 Zeichen:17
+ ...             Publish-PSArtifactUtility @PublishPSArtifactUtility_Param ...
+                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (:) [Write-Error], WriteErrorException
    + FullyQualifiedErrorId : FailedToCreateCompressedModule,Publish-PSArtifactUtility