Hello @Fuhrer Jean-Pierre ,
I understand that you are trying to deploy a VPN gateway in "Germany West Central" region, and it fails with an error "VmssGatewayDeploymentFailed".
I tried replicating this issue in my lab and received the same error.
I checked internally and found other customers reporting the same issue.
It is an ongoing issue with VPN gateway deployments in "Germany West Central" region. And the current workaround is to create your VPN gateway in another region.
Kindly let us know if the above helps or you need further assistance on this issue.
Please "Accept the answer" if the information helped you. This will help us and others in the community as well.