Hi Katharina-Maria,
Yes you are correct the IEMV supports one interface and that is the case for the foreseeable future. You can find this stated also in the documentation website:
https://docs.eu1.edge.siemens.cloud/get_started_and_operate/industrial_edge_management/v/introduction/requirements.html
Also for IEM-ISO it is required to have a single interface not multiple ones as this is not native supported by the underlying architecture