Rather than rotating the canvas permanently, you can rotate the document view 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 document view rotation
Being able to rotate the document view 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 document view:
From the View menu, select Rotate Left or Rotate Right. The document view will be rotated in 15 degree increments.
From the same menu, select Reset Rotation to reset the document view back to its original rotation.
To switch off/on document view rotation (for Trackpads):
From Affinity Photo>Preferences (Tools option), uncheck or check Enable Canvas Rotation with Trackpad.