Outline stroke: line to shape
A stroke cannot cut other shapes. Outline stroke turns it into a filled shape that can.
Try this
- Right-click the top wave and choose Outline stroke. It looks the same but is now a filled shape.
- In the third row, that shape cuts a bar. Click the bar, open Modifiers, then Combine.
- Right-click an outlined wave and choose Release outlined stroke to get the stroke back.