Taking a PSD and importing into Affinity Photo (trial) can result in vastly different visual appearance if the file relies on how "fill" works in Photoshop as opposed to "opacity". In Photoshop-land, fill performs a blend mode-specific modification to the input values or to the blend equation to moderate the effect of the blend mode. This is quite noticeable when using the "hard mix" blend mode which when adjusting fill, in Affinity, seems to linearly interpolate between simply passing through the bottom layer and displaying a full-intensity version of the blend mode. In Photoshop, this seems to instead to modulate the intensity of the blend mode itself, making the burning and dodging effect far more manageable.