Affinity Photo Fade Filters Tutorial
You can apply a filter effect and that is that, no, you can reduce the power, you can enhance the effect by using the layer menu and fade. You can also use it with many different effects such as gradient fills and much more. This means you can set the opacity etc
The panel always has two options, the opacity of the effect as well as the blending mode between the effect and the original image. You can set it between 0 and 100 % and also you can set the blend to difference, darken, lighten, color burn etc
So how to use it, go to the filter menu and apply an effect and go to the layer menu and fade command - it will list the effect used. Apply the effect and go to the layer menu and select that command and you will see the setting by default at 50%. Set to 0% and you will see none of the effect, set it to 100% and you will see only the effect and not the original image. You can also introduce a blend mode such as lighten or darken. If you set a blend mode then you see at 0% the original image combined with the effect and the blend, set to 100% and you don't see the blend mode. It is slightly confusing way around to my mind.
You can also go to the layer menu and repeat it, over and over, though at some point it becomes a little meaningless but certainly for one or two repeats, the result can be interesting
You can apply a tool such as the gradient tool and still go to the layer menu and again reduce the effect, you can set the gradient to 0% or 50% or 100% and again use blend modes such as darken or lighten.
Go to one of the brush tools and then select a preset and apply the stroke to the current art board. Once you have applied it, you can go to the layer menu and reduce / change the blending mode of the applied design. Works best when you have applied a lot of brush strokes to the image and then use it as just applying a few, results in very little actual impact. You can also use it with the smudge as well as other tools. The key thing is that you use it as soon as you have applied the stroke otherwise it will be lost.