I am not the creator of that topic, but I have the same problem. If it is not okay, that I write here, give me a sign, please. This is my first content.
I tried the RGB and CMYK color palette in every program of Affinity but I got also an creamy white (touchy yellow). Here is my sample. I Work with Windows 10 and in the screenshot you can see the Affinity Designer original file and the exported pdf. This is a really great difference, don't you think? What can I do to make white really show up as white?
Thank you in advance for the support.