Rather than rotating the document, you can rotate the canvas instead, which is akin to physically rotating your working space. This allows you to view your document from a different angle without manipulating its layout.
About canvas rotation
Being able to rotate the canvas is beneficial for a number of applications:
Brush and fine detail work
Product design (e.g., product box/packaging layouts with content at 90/180 degree angles)
Tablet-assisted design (drawing at angles)
To rotate the canvas:
From the View menu, select Rotate Left or Rotate Right. The canvas will be rotated in 15 degree increments.
From the same menu, select Reset Rotation to reset the canvas back to its original rotation.
To switch off/on canvas rotation (for Trackpads):
From Affinity Designer>Preferences (Tools option), uncheck or check Enable Canvas Rotation with Trackpad.