Affinity Photo : How To Mosaic Pattern Effect Tutorial
Basic line / tile
Create a basic line using the pen tool and hold down the shift so initially it is a straight line. You can then go to the stroke settings and go to the third item and select the dash line style panel for the color for the stroke and create your initial mosaic tile (in any color, you can always vary this later).
Dash / Gap
You can then go to the dash / gap settings at the bottom of the panel as well and set to 1 and 1 as well as set the cap settings to the 2nd option. This can be used to create all kinds of amazing different designs and you can also enter decimals, so you don't need to use 1 and 1, you could equally use 0.5 and 0.7 etc.
Once you have your initial line, you can use the node tool to warp and distort this line to turn it into a curved line and you can change this in all kinds of directions. You can modify the nodes as well as the handles to create all kinds of unique forms, select and drag.
The line can now be further modified by using layer effects styles which can be added to the stroke via the FX button at the bottom of the layers panel. You can then add a bevel / 3D etc effect to your design as well as an outer shadow. You can now go to the layer menu and rasterize, deselect the fx entry in that panel.
The artwork can now be turned into a pattern via the layer menu and pattern layer from selection and you can then re-size, rotate, etc as well as duplicate the layer and add multiple layers in the same color as well as adjust the color by using layer menu and new adjustment layers such as HSL applied to that particular pattern.