The base plate allows moisture to rise upwards

We bought a completed house from Team Massivhaus. However, no one has ever lived there. Now we are noticing rising damp inside some door corners and are wondering if the external sealing of the floor slab is correct. Does anyone have experience with this?

The sealing would be under this foil. Therefore, it cannot be said. The question would also be for which load case the sealing was designed. Often, it is sealed only against simple moisture, but not against standing water.

Take your documents from the construction (if available) and get an expert who looks at the matter on site. If there is still a warranty on the house, you can then complain to the builder with the expert's report.