In the final episode of season 2 of the the Mandalorian (“Chapter 16: The Rescue”) Moff Gideon makes a big thing of the fact that…
…the Darksaber cannot just be passed on but needs to be won by defeating it's current rightful owner. For this reason Bo-Katan is not able to accept it when offered to her by Mando.
Why then it was previously passed from Sabine to Bo-Katan — during the Rebels series — in what to me seem like very similar circumstances.
Disney canon answers preferred, but I’m also interested in any relevant information from Legends, especially when it doesn’t contradict Disney canon.