However, your intuition is correct that the crucial difference arises during the deceleration at Canopus and the lack of a return journey. In the original paradox, the traveling twin's acceleration, deceleration, and return trip introduce additional effects not covered by Special Relativity alone but by General Relativity. The traveling twin's turnaround involves changes in acceleration $($including deceleration$),$ which breaks the symmetry of the situation. It's this acceleration that allows us to distinguish the non$-$inertial $($accelerating$)$ frame of reference from the inertial $($non$-$accelerating$)$ frame of reference of the twin on Earth.