From my testing, it seems you need to provide people Contributor/Member/Admin to the workspace with the dataflow. If you choose the lowest permission Contributor - then they can't edit the dataflow BUT they can take over ownership and change the scheduling ! Not Good.
I just want people to be able to connect to the dataflow.
Not sure what i did wrong in my initial testing, but did it again and it was as you say.
Viewer gives them rights to connect to dataflows from Power BI Desktop.
Perfect - exactly what I wanted cleared up.
I still think its a bit strange that I couldn't find any MS arcticles or guidance that specifically covers this pont of how to provide access to dataflows ! Maybe it was meant to be really obvious and no guidance was needed !