Affinity's light mode UI — in the document setup — has been giving me a headache for months. When you set proportional dimensions, the icon disappears, or becomes so light that you can't see it. And the anchor/rescale active states are reversed. When you chose rescale, the rescale option is greyed out and the anchor option turns white. Which is also wrong. I mentioned this to support months ago, but nothing came of it. Just pointing it out again because it's become highly annoying and time-consuming.
The attached screenshot is what it looks like when you set proportional resizing and rescaling. Looking at it, you wouldn't have a clue.