Well, you start from something super simple, a white rectangular shape that fills the entire image. You need something to work with, you could also have a black shape or green or blue shape up to you but the add noise filter needs something to apply to and the rectangle is a great option.
The next step is to fill the layer with an effect, the add noise filter which can be found in the filters menu and noise. Apply it with a high intensity setting with either uniform or Gaussian setting. You can apply it more than once via the repeat option at the top of the filters menu.
Still not particularly a liquefied distorted warped image of lines at this point but now you can use the deform filter which is found via the distort menu in filters. Start that up and you can add pins. I would suggest multiple pins and add them all over the image, sometimes close and sometimes not and also set to similarity (though rigid is fine). Drag the pins to distort and deform the noise and as you do this with the pins you will see the noise is stretched and warped and distorted and liquefied. You can repeat this. I would suggest always dragging outwards otherwise you will end up with transparency and breaks in the layer which is now a pixel layer and not a vector layer. Apply the deform. https://youtu.be/2Y1caGvK3-E
Repeat the deform filter three or four times to really stretch out that noise in the layer. The noise will now be turned into streaks of warped lines.
If you want, you can also select a part or all of the layer and then go to the layer menu and new pattern layer from selection and I would suggest then you go to the move tool to re-size and rotate etc the pattern layer as well as go to the mirror option in the top left of the app and turn that ON.
You can now move the pattern layer around and you will notice the layer and lines are warping in all kinds of ways. You can also apply the deform filter again to the pattern layer itself and see how the pattern seamless tile of the liquefied warped lines change and change as you move the pin designs as well as change the pattern
You can repeat all the above on multiple layers with different levels of grains as well as different levels of deform and then you can combine all those layers with blending modes and opacity.
All the above can be captured into a macro via the view menu and studio and macros and with that macro, you can re-apply all the deforms etc to any set of noise designs in Affinity Photo to create different stretched and warped artwork. https://youtu.be/xoXlRitpEA4