Even after Steinberg asserted Sierra qualification for Cubase, this seems to be a bug/quirk that I discovered.
- Make a new Cubase project and have at least 2 windows open (ie: Project window, MixConsole, Tempo Edit window)
- Save the project and close it.
- Quit Cubase
- In macOS Sierra System Preferences → Dock → “Prefer tabs when opening documents”, set it to “Always”
- Run Cubase and open that project.
All the open windows will be merged into a single tabbed window. It doesn’t seem to negatively impact performance, but the tabs are grey and washed-out (which indicates that it hasn’t been implemented ideally), and it obviously is undesirable for projects where you have meticulously opened and positioned various windows across your screen(s).
The Steinberg macOS dev team could add some code that deals with the new Sierra window tabbing more elegantly (or disable/sidestep it for Cubase through some code.)