Affinity photo will open an equirectangular image, which displays flat. It has a feature that takes this type of image and can do a live 360 projection, this allows you to pan around your image and adjust. Once you have finished making your adjustments you then exit the projection so the image converts back into its original equirectangular mapping (displays flat), so you can export it.
Some image hosting sites and other programs will have support for these type of images so they can be viewed in the same way, allowing you to pan around the image.
