You can create dashed lines by editing the advanced stroke options of any shape.
First select the shape/line:
Click on the three dots under the Stroke options in the Properties Panel to open the Advanced Stroke options
- You can then enter the size of your desired dash in the following field, the first number is the size of the dash in pixels, followed by the size of the gap.
Note: the start and end of the dashed lines will be half the size of your dashes.