You can create the Affinity Photo pattern layers from any pixel design / selection, create a gradient, open an image and then define one via the pattern layer from selection. Once you have that tile, you can remove the underlying design if you wish and then re-size the pattern and rotate the design.
You can see the bounding box for the tile and you can use that with the rectangular marquee or ellipse or freehand and just create your marching ants around part of the image as long as it overlaps with the bounding box of the tile. You can also add / subtract etc from it to create all kinds of unique artworks however there must be at some point, some overlap with the actual tile bounding box.
Copy and paste using the edit menu and now you have a new tile design, you can re-size that and rotate that design, it can be used in the same way as the source. You can also shift it and go to and select both tiles.
Go to the merge selected command. You can then repeat the process.
You can also simply use the alt / opt and drag to create multiple copies of the small tiles and rotate and re-size and shift them and build up a complex design made of all these fragments. Again, they are all as before, tiles that can be merged and you can then continue to work with the artwork.
Go to the artistic text tool and set a font and set a size and create some random letters, recolor some of the letters etc. Go to the layer menu and rasterize. Goto the elliptical marquee tool and set the feather setting as required and make a circle marquee over the text and then go to the command to create a new tile. As always, unless you want to keep it, delete the original. Resize it and rotate the bounding box. As it will have some transparency (being a circle), you can also hold down the alt / option key and duplicate it. Go to the layer menu and merge visible. You can now again do the same with the elliptical marquee tool and create ever more complex tile designs.