Application using Microsoft.Graph.dll works on Windows 10 but doesn't work on Server 2019

• The "program" is a Windows-Service developed with .net/C# (Framework 4.8) VS2022.
• But this is no factor on the issue. The "bug" can be reproduced with a simple console application.
• The "program" uses MS.Graph.dll to communicate with Microsoft365 (e.g. @int.sg.ch or @2vgwn2.onmicrosoft.com for development)
• The program performs requests on users inboxes and calendars
• It's authenticated via a registered app in the cloud and this app has all needed rights
• No exceptions/events are present in the EventLogs on the Server

So:

• The program works well on Windows 10 (in all aspects!)

• The program is not working from Windows Server 2019
  o More detailed: The request via the MS.Graph.dll results in an unspecified http-request exception (after about 1 minute).
  o I have build in the same request as raw http-request and that works perfect (on Windows 10 and Server 2019)

• We have already excluded following issues on the Server:
  o Internet/Porxy access (I can do requests from e.g. POSTMAN to the Graph-Rest-Service, that works as expected)
  o .net Framework 4.8 and dotnet 8 is installed and works
  o Authentication works, access token is valid and works an both Platforms (Windows 10 and Server 2019)

The remaining component therefore seems to be between Server 2019 and the dotnet MS.Graph.dll library(s). Something on the Server prevents the work of MS.Graph.dll's

Start with the simple console application on Windows 10 and Server 2019, comparing the Microsoft Graph SDK request with the working raw HTTP request. Capture the unspecified HTTP exception and its inner details; done means identifying why the SDK request differs or documenting the server-side cause.