Sorry jamessouttar, as far as I am concerned that is a bodge of an answer.
When setting up a new document I expect to set the size, pages, facing, columns, margins, bleed and slug in one go. I would also expect to set set the bleed in one side and all the others to match. Unless I missed this, I had to put in all four separately. As yet I have never found the requirements of any work I have done to have separate bleeds for different sides.
When I work on a document, I want to see the bleeds. I don't expect Affinity Publisher to have all the features of InDesign, that would be unfair but do expect something as basic as this.