This is an issue of the Windows App SDK, but it's by design. There would be a way to use file pickers that work on elevated permissions, but I'm not sure if I want to use it, as working with locations that require elevated permissions, is not good for modding and I suspect that the solution has its flaws.
(The alternative would be to use the GUI in a sandbox environment, where users would have to give permissions for file access, but this would still block write access to protected locations, so I'm not considering that.)
This is an issue of the Windows App SDK, but it's by design. There would be a way to use file pickers that work on elevated permissions, but I'm not sure if I want to use it, as working with locations that require elevated permissions, is not good for modding and I suspect that the solution has its flaws. (The alternative would be to use the GUI in a sandbox environment, where users would have to give permissions for file access, but this would still block write access to protected locations, so I'm not considering that.)