Cyclone DDS Supported in Dashing?

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I am a bit confused if cyclone dds is supported in dashing...
Installed it like described here.

The demo talker / listener is working, so it should be in the list of supported rmw implementations.
But when I want to build my workspace and do --cmake-force-configure or even clean my workspace and rebuild, I always get:

The RMW implementation has been specified as 'rmw_cyclonedds_cpp' through the environment variable 'RMW_IMPLEMENTATION', however it is not in the list of supported rmw implementations, which was specified when the 'rmw_implementation' package was built.

And I think the message is wrong, because the installed demo_nodes_cpp talker/listener is working, so it has to have support!?

My system:
ROS Dashing, Ubuntu 18.04