Brush Pressure controls opacity is the one missing feature in Affinity Designer that is keeping me from making it my main paint app. I can't find a way to change opacity with brush pressure. If the feature does exist I'm not seeing it. Seems like it should be under the dynamics section of the brush editor. The attached file is one I sent to Paolo Limoncelli which illustrates the issue. He was able to help me with advice on blending, but I miss my opacity control which is available in virtually every other paint program known to mankind. So, if it is available I'd love to know how to do it. If it's not then it should be a top priority for your next release :D