cannot open project from project tab in version 6
Which version of which tool?
System Workbench for STM32 is in version 1.4.0 (1.5.0 is due next week) while CubeMX is in version 4.10, so I really don’t understand what is your problem...
Anyway, in System Workbench, if you want to open an existing project file, you can’t just open it as a file, you must import it in your workspace, using the “Import...” menu item, either from the project explorer contextual menu or from the File menu.
Bernard