Why is there no current flowing through the relay coil in this Qucs 0.0.19 simple dc circuit?
In QUCS the relay (or relais as it is called internally) is a voltage controlled switch.

The primary side has infinite resistance when it is engaged or not engaged. When there is enough voltage across the primary it will close the secondary

https://github.com/Qucs/qucs/blob/develop/qucs/qucs/components/relais.cpp