spoilers for The Clone Wars, Rebels, and The Mandalorian season 2
The Darksaber is established as being forged by Tarre Vizsla and then passed down through the Vizsla clan. This shows that the Darksaber can be peacefully passed, and it stayed within the Vizsla line, as Pre Vizsla is the one wielding it in The Clone Wars.
According to the rules of the Darksaber, Maul became its rightful wielder and the ruler of Mandalore when he won it from Pre Vizsla in combat. From here, its path becomes looser - no one wins it from Maul, but Sabine steals it from him. Then Gar Saxon steals it from Sabine, and Sabine fights him and wins. While the Wookieepedia page says that this made Sabine the rightful wielder of the Darksaber, this doesn't seem to be confirmed, as she didn't technically win it from its last owner.
Despite all of this, when Sabine offers the Darksaber and the rule of Mandalore to Bo-Katan in Rebels season 4, Bo-Katan willingly accepts it. Season 2 of The Mandalorian says that the Darksaber can only be claimed in combat, but this is at odds with the passing of it from Sabine to Bo-Katan.
I've heard theories that, since the Darksaber was never technically Sabine's, she passed it on to the next person who it would have gone to - Bo-Katan, who was second-in-command next to Pre Vizsla.
Is this why Bo-Katan accepted the Darksaber from Sabine - because it would have naturally gone to her? If it is the case that Bo-Katan would've taken the Darksaber after Pre Vizsla, then maybe it's about that, instead of having to fight for it? Clearly the Darksaber can be peacefully passed down, as it stayed in Clan Vizsla for years.
It is interesting that Bo-Katan accepted the Darksaber under these circumstances in front of all of Mandalore, whereas in The Mandalorian she refused to despite not having any witnesses.