Red Alert 3 Decimation Map Pack on Xbox One Backwards Compatible does not work.
Me and a friend both have Red Alert 3, I have it on disc while my friend bought it on the Xbox One store. He got the Decimation Map Pack for it when he could, but even though it was installed, and many other measures were used, the maps never showed up. My disc version, however, worked from day one on Xbox One. We went through every step under the sun and even Xbox Support told us it was an issue on EA's end.