I see, so this confirms that WoA cannot emulate Affinity Photo since it's targeting x64 architecture. I haven't delved into it that thoroughly, but this might be promising for recompiling with ARM64 as the target. Hopefully the ARM64 SDK implementation covers what Affinity Photo depends on from the x64 SDK.
From a previous BUILD conference (https://www.neowin.net/news/microsoft-finally-releases-an-arm64-sdk-supporting-uwp-and-win32-apps/)
Microsoft is trying to suggest it wouldn't be too much work to recompile for ARM64. Of course, I don't know how complex the Affinity codebase is, so probably an engineer can better assess if any extra work is required as TonyB suggested.
But I do have my fingers crossed