Following the steps provided on the website https://wiki.event-b.org/index.php/Atomicity_Decomposition_Plug-in_User_Guide, the "flow diagram" button cannot be found in the step “Creating Flow Diagrams
Then a flow can be created:
1. Either for an Event-B machine, when right-clicking on the machine. ”
This is my display interface.
One of the developers of the plug-in confirmed that it is unmaintained and does not work with recent Rodin releases.