Hi Jan,
this issue is currently being investigated – see https://status.mendix.com/
Update - We are investigating the issue.
May 27, 10:48 CEST
Investigating - We have observed and are investigating degraded performance of the Developer Portal. Customers with apps running on SAP BTP are not able to create new deployment packages. You are able to deploy existing deployment packages
May 27, 10:46 CEST