The anti-aliasing is what is happening automatically, and what I'm trying to avoid, which is possible depending on what resampling technique is used (Photoshop allows you to choose the resampling technique just about anywhere in the app for this exact reason, between Bilinear, Bicubic, Nearest, etc.). But Affinity Photo doesn't appear to allow that to be changed in these key areas (merging or rasterizing layers). I'm working on pixel art (very small-resolution bitmaps) which I wish to use a Nearest Neighbor filtering mode. This can be achieved in the Performance settings but only appears to impact the display of layers during editing, and merging them down applies the anti-aliasing without any options on what resampling technique to use.
Thanks for the suggestions, I've tried Force Pixel Alignment and also making use of the blend ranges options but that doesn't solve the problem. What is happening is a very visually-obvious blurring when layers are merged or resampled. This blurring is a result of the filtering technique used under-the-hood; I need the option of using a Nearest Neighbor algorithm. I understand that 99% of Affinity Photo users don't want this, since in large-pixel documents the anti-aliasing provides smoother and more pleasing results. But for pixel art it causes the artwork to become blurry and distorted which is not desirable.