@ralf_wegmeth
Can you please try this?
0. Uninstall Fusion
1. Make sure that Fusion installer is not running in task manager
2. Go to %localappdata%\Autodesk\ then DELETE the following folders – Webdeploy, Web Services, Identity services, Autodesk Fusion 360 ((IF you do not have any other Autodesk products installed, delete the Full Autodesk folder)
3. Delete the shortcut that is used to launch Fusion
4. Restart your machine
5. Do not use the same Fusion installer. Can you please download the installer again
6. Now install again
