How To Use Average Filter In Affinity Photo Tutorial | Graphicxtras
The average filter in Affinity Photo can be found in the filter menu under the blur menu category
It can be used with all kinds of images as well as the presets. It is only found in the filters menu, it not available as a live filter layer unfortunately (not all are). It can be used on all images and if the image is fairly bluish then the end result of the blur will be a solid blue which does not sound very useful.
You can combine it with the layer menu and fade so the effect can be faded with perhaps a different blending mode as well as opacity and the end results are not just a solid color but often stunning colorful designs.
Another alternative is to duplicate the current image and then apply the effect to that and then use the blending modes to blend the original and the effect. You can also use the layers panel with a duplicated image by using the background image and re-sizing and reducing the top layer and then apply the effect to the background which creates an instant frame
It can also be applied to a channel, so go to the channels panel and select the red channel and then apply the average blur to that either by using the repeat option or using the blur menu category. You can also use the layer menu and fade and blending modes. Select the green channel in the channel panel and do much the same but perhaps use a different blending mode. Restore to RGB by using the button at the top of the channel panel.
You can also use selections, use either freehand or perhaps some of the selection menu commands such as tonal etc and then apply it to that and move the selection and re-apply it to that new selection.