You can find it in the blur menu
The Affinity Photo median blur filter is great with low values for noise, it is also great for color blurs and edges. To use the effect, goto the Filters menu and Blurs and Median blur and Set radius and Apply. You can apply a subtle radius as well for a more interesting effect
You can use it more than once. If you want to repeat the effect, set the radius to a reasonable value and then repeat. You can apply the repeat over and over to create all kinds of unusual effects
You can fade the effect via the layer menu and fade and set a different blending mode as well as opacity
It can be used with others, you can combine it with other effects via the macro panel. Find the macro panel via the view menu and studio. Start recording the effect as well as combining with others such as deform etc. You can then apply the macro over and over and you can also save it your library and re-use in future projects
You can also use the effect with color channels such as red channel, green channel etc Go to the panel and select the red and then go and apply the effect with a setting, repeat this for the green but use a different setting and likewise with the blue. Of course, if you are using CMYK then you will have the cyan channel etc instead. You can also just apply it to one.
You can also use it with selections, all kinds of different selections. You can use any number of selection tools to add the selections and it can be applied to those or the inverted or feathered etc
There is no option for this, for some weird reason.
You can create a layer, a new design or perhaps a duplication of the image and scaled and then apply the effect to that
You can add text as a layer (frame text as well as artistic) and apply it to that. You can use the effect with the text as a layer and create some very rough distorted text in seconds. You can also flatten the text with another layer and use it on that and the result will be different
The effect can also be used with the powerful pattern layer from selection. Apply the effect to the image and then go to the layer menu and pattern layer from selection command and you can then re-size the layer with the effect as well as rotate and you can also set the mirror option to On and create amazing seamless tiles with the effect.