Flying from London to the west coast goes against the jet stream, so range is shortened by flying into the wind. Transatlantic routes that are currently using narrowbodies will sometimes have to divert for a fuel stop when the jet stream is particularly strong.
The official website for this aircraft doesn't seem to suggest that, for example all of California is outside its range graphic:
https://aircraft.airbus.com/en/aircraft/a320/a321xlr
I'm not able to use that gcmap website linked.