The dropdown to open a Project in a scheduler (Workbench or Microsoft Project AND PPM Gantt) does not do anything in the new UX, not even displaying the PPM Gantt option, unless a Scheduler Format has an assigned (non-null) value.
Steps to Reproduce
Expected Results: PPM Gantt option is displayed.
Actual Results: Nothing happens (not even a warning/error message) after clicking.
This issue has been logged as DE38192 to Engineering.
This issue has been fixed in CA PPM 15.4.1.
Even if you are not planning to use any external scheduler (such as Open Workbench or Microsoft Project), select any of the two as the Scheduler Format for the Project (normally found under Project's Settings).