Slurs automatically cross system breaks and frame breaks, appearing in two parts on either side of the break.
By default, the endpoints of slurs that cross system/frame breaks are positioned at least 1/2 space outside the outer staff line and at a suitable position based on the pitch contour of the phrase before/after the break; that is, indicating whether the phrase rises or falls after the break.
If multiple slurs cross the same system break or frame break, such as if a phrase split by a break contains nested slurs, the ends of the slurs are stacked automatically and spaced a minimum of 1/2 space apart vertically.
You can determine whether or not Dorico Pro adjusts the vertical endpoint positions of slurs based on phrase contours in the Endpoint Positioning section of the Slurs page in Engraving Options.
In Engrave mode, you can move and edit each slur part separately. This allows you to adjust the start/end height of each slur part independently on each system.