Insert divider between two flows - help

Please how can I insert divider between two flows. As I created score where there is few bars with only strings section playing, then it goes to full orchestra. To make this possible I need to split main flow to three flows. And I need divider between second and third. Is it possible? Or it works only within one flow? If yes, how can I manage this situation? thank you

There is Write > Split Flow. But you don’t have to split the flow in order to hide all the empty staves in the middle section. See Hiding empty staves in the manual.

What kind of divider do you want? A new page? You can make a frame break in engrave mode.

That helps, thank you