DE-"calls" are not issued by BNetzA, the German licensing authority, but by the DARC e.V. , the German Amaterur Radio Club.
They are simple SWL calls and don't allow to transmit or to build a transmitter.
All info (in German) is available at https://www.darc.de/funkbetrieb/kurzwellenhoerer-swl/.

Club Log maps DE calls to "INVALID", meaning the calls are not valid for DXCC.

Acknoledgement
Axel Schernikau, DL6KVA