Thanks for the answer.
An interesting idea with clouds and the Displace option, but it does not give a good result. At least that's my opinion.
I used a few pics of clouds that I found on the internet in high resolution. Those where there are several clouds and where the whole sky is covered. As the effect was poor, I decided to make the clouds myself thanks to the Perlin Noise in Affinity Photo (Filters / Noise / Perlin Noise) option, something like Render > Clouds in Photoshop.
Well, the quality is definitely better, but the main problem is that this option makes the image or text jaggy/ragged not jittery/wiggly. I do not know if it's a matter of the "Pixel" layer and because of that it's loses on quality, and if it would be on the vector image it would work ...
Of course, I used a small effect of "Displace" (like 20-30 was max because of noise / jaggy)
I checked if I can draw something in Affinity Designer in a vector (by the way, can I connect them somehow? I wrote two words and I had lots of layers that I could not combine into one.) I moved work back to Affinity Photo, but unfortunately the option "Displace "requires a raster layer ...