On Vudu, Movies Anywhere, Fandango and Google Play there is a filter to show purchases alphabetically. This feature is available when viewing Prime Video on my computer but not when viewing On Roku...Can the app be fixed to add that filter?
That is only something that Amazon can do. Roku does not create the channels available on their devices, other than The Roku Channel. The providers are the only ones that can make changes to their channels. You'll have to contact Amazon for that.