There is no option to create a new BPMN 2.0 diagram from within Explorer
Image/data in this KBA is from SAP internal systems, sample data, or demo systems. Any resemblance to real data is purely coincidental.
Please check with your workspace adminstrator that you have the correct access rights to create a new diagram.
KBA , BPI-SIG-CA-SEC-UM-AM , Access Management for SAP Signavio , How To