I might understand blend mode wrong. But I always believe when we set white pixel's blend mode to "multiply" they disappears. At least this is how photoshop handles it. I found this explaining multiply mode in photoshop https://theeagerlearner.com/your-big-friendly-guide-to-layer-blend-modes/
"Multiply – This is what we use most often when we want to make things darker. White is invisible, black is opaque & the grey is making things darker."
While on Affinity Designer, multiply "always producing a darker value." https://affinity.help/designer/en-US.lproj/index.html?page=pages/Layers/layerBlendModes.html?title=Layer%20blending
See https://imgur.com/a/fgCWOEC, left shadow has blend mode normal, and right shadow has blend mode multiply. The white pixel also makes the ground darker.