Check out this video, at the 4:20 mark he demonstrates how the seats move with the keyfob. He doesn't mention what year Denali it is but its clearly a 2015 - 2019.
I don't buy that the feature was taken away as the dealership told @George100.
Edit: I asked the person who created the video what year what his Denali was, its a 2015. I would imagine the newer Denalis *should* have the same functionality.