The minimum blur filter for Affinity Photo is a powerful tool found in the blur category (filter menu command).
Great for really smudging and darkening any image or resource. It can be used with images as well as resources / presets. You can use the effect with images as well as text and also with type / text.
The effect can be used with color channels so you can apply it to the red channel etc. You can then use it in the green etc with a different darkening setting to create truly weird and wonderful effects. You can also use it with an alpha channel and apply the effect on that as well. https://youtu.be/shr_2G9BlnM
You can also apply to a limited part of the image by using a selection by going to the rectangular marquee tool etc and then creating a quick selection and then using the effect with the selected or you can also use the select inverse command and then apply the effect to that area.
It can also be used with multiple layers and more and with that, you can then also use the blending modes to blend between the layers such as adding in linear burn, color burn, difference, overlay etc.
Set it with a very low value and you will mainly see darkening around the edges to create a sort of dark cartoon effect. Set the value to a higher value and you will see more and more black and less of the image, giving the impression of smudging around edges. The higher values, I think the circular option is a far better choice. If you push the value too high then the image just becomes black. You can enter a value into the radius setting or use the sliders or interactively drag across the image to apply the effect.
As with all of the others, the effect can be recorded via the macro panel and also saved to the library for future use. You can then use the same effect over and over in the future as well as modify the parameters (so making it even more useful) https://youtu.be/xoXlRitpEA4
You can fade the effect. Instead of using it with the full force, just go to the layer menu and use the fade with 0% or 50% etc as well as change the blending mode. You can create all kinds of amazing combinations with the darkening effects in this tool with that option. https://youtu.be/SiFQ3abvyiI
Create some large text (in black), say the word text at 300px and also create a background rectangle (in red) to fill the entire image (or certainly bigger than the text). Go the merge visible and you should end up with a pixel layer with your text and rectangle combined. Go the live layer category in the layer menu and select the effect. You will see a panel marked live with the effect name and radius and circular. Turn the circular to ON and increase the radius using the interactive left to right slider or control (say to 20px). Set the opacity to 50% and you will see a contour with the enlarged text and the original pixel text. Repeat this an add another of the live effects and set to 50% and radius 20px and close. You can repeat this for a few times and you will end up with a contour text effect