There are a few ways to crop / hide text in Affinity Designer. Using the mask feature with the shape tools and the generated text as well as using the vector crop tool which can also be found in the tools panel.
Create some lines of type etc or create in another document. Go to the shape tools such as the heart shape or the arrow shape and create a shape design and this is a vector so can be any size or angle. Select the shape in the layers panel and drag onto the thumbnail of the text in the layers panel and the characters (more than one) will be masked. You can then select the heart shape or arrow shape in the layers panel and manipulate the shape with either the shape tool to change the properties such as the arrow heads or you can go to the move tool and then rotate and shear and scale and move the masking design. You can also select the characters (above the shape in the layers panel) and then manipulate the size etc of that as well.
You can select the characters (frame or artistic) and then go to the vector crop tool and the design will then be surrounded by the crop bounding box which can be re-sized. If you go to the layers panel you will notice that the characters now have an entry beneath (slightly to the right) and it will be a rectangle. You can select that rectangle and then with the move tool you can re-size and remove more or less characters and you can also rotate the box to create all kinds of different crops. With the rectangle selected and the move tool, you can go to the convert to curves button and turn the artwork into curve which can be manipulated by the node tool. The rectangle can now also be modified further by tools such as the contour tool to add an extended edge (or cutting into the characters) to the art and this can also be manipulated further by using layer styles via the layer menu.Youtube video on subject