You want to create straight lines, lots of them, very quickly and efficiently
The key filter for this tutorial is the powerful procedural texture filter and this can be found in the Affinity Photo filter menu and color. To use it, firstly work in RGB (you can always convert later to CMYK) and then add a new layer via the layer command and then go to the fill command and fill it with something or perhaps apply a gradient, it just needs some content. Go to the filter and in the panel, go to the presets in the top right of the panel and select a preset, the best one being 'waves'. If you are using CMK then the waves filter will not be visible.
You will see an equation for the waves filter, please select that and use that as a start point. You can then go to the ry entry and instead of using ry you can replace it with 30*ry or 20*ry. the higher the value, the more entries in the end result will be generated. You can also modify the ry to rx and rx to ry. If you want to create a diagonal version then use ry + rx or ry - rx. You can also make many other variations such as 2*ry+rx or ry*rx etc
If you leave the a setting in the middle then the lines will be wavy, if you want the lines to be straight then set the value to 0. You can also vary the settings in the equation and add additional custom inputs such as reals and integers
The result will be a set of lines. The number will depends on the factor applied to the ry or rx setting. You can then add additional effects via the filter menu such as deform and mirror. You may prefer to use the new mesh warp feature in the filter menu or use it in a non destructive way by applying it via the layer menu and live filter layers
If you re-apply it again to the same layer then the result will be exactly the same. You can re-apply the effect to different layers. You can re-apply it via the top menu item in the filter menu. If you want to combine it with the underlying layer (and that can be a solid color or an image or text) then go to the layer menu and fade the applied effect and perhaps use a low opacity setting along with blending modes.
You can also create exactly the same if you use the layer menu and live filter layers and procedural texture. You can apply the effect to the underlying layers such as shapes and text