Is there a way to move bars between systems in just one part? Engrave mode shows all the parts, so I can’t change anything in just one. This was so easy in Finale.
Okay, I figured that out. But how do I force measures into a system?
Got it. Thanks so much. It’s kind of counterintuitive, but it works.
I added that you can select something and create a system break (like new line). Same menu, or Shift-S in Engrave mode. Shift-F for Frame break. (like new page)
Jesper
Okay, now a new problem arises. I want to move one bar to the previous page, but I can’t select items in that bar along with items in the system I want to move it to without selecting items in many other bars.
Yes, it worked. Thanks.
Coming from Finale you could mistake counterintuitive with unfamiliar 
And please consider that Dorico provides much more powerful layout options than just movings things around like in Finale.
Just two specific items will do: one in the bar that you want to be the start of the system (or indeed frame / page), and one in the bar at the end. You can Ctrl/Cmd-click just those items, for example. The material inbetween doesn’t need to be selected.