-
There would need to be Saver level availability with AA to see it bookable on BA with Avios.
I’m not sure where you’re seeing “Book and upgrade”.
All of the nonstop AA flights on those days are in the 40k range, which is not Saver level.
The Saver level flight below is 11.5k AA miles but has a stop.
BA is not always good at piecing together AA segments so may need to book separately.
BA is a per-segment award program though, so will be ~2x the points needed for the NS saver you’re seeing.