The Affinity Photo spherical filter can be found in the distort category of the filter menu and is a destructive effect to warp images as well as other resources in the application such as patterns and brushes and text and decorative font designs and more.
Set intensity and set radius and set origin point and then apply
You can fade the effect (though it doesn't reduce the size of the sphere) via the layer menu and the fade command. The fade means you can change the opacity of the effect along with applying a blending mode to the effect such as difference, linear light, pin light, average, exclusion to create even more unique designs.
You can apply the effect once and you can apply it again and again, though at some point it will cease to have any real effect as this is one that reaches a limit of how it can distort a layer or image.
You can add the effect to an image and then go to the layer menu and create a pattern layer from selection and the effect will then be seen as a repeat pattern. It works best if you go to the mirror option at the top left and set that on. The pattern layer can have other effects added as well and can also be rasterized via the layer menu and rasterize command. If rasterized then the artwork can then be modified further
It is a destructive effect though, distortion or otherwise, you can undo the result via the history panel. You can also apply a non-destructive effect to the underlying layer or the current active layer but it also additional features mean it can be faded via the opacity as well as the blending can be modified to be darken or difference or pin light etc. Another great option is that it can be changed at any point by going to the layers panel and double clicking the entry.