Who was it to betray soma?
Once interacted with Soma you will then have to select one of the traitors, between Birna Lif and Galinn. It is precisely the latter, Galinn, who turns out to be the only correct answer to this particular puzzle.
Eivor can investigate who betrayed Soma, either by searching for each of his allies, or by simply investigating the land around Soma's settlement, Grantebridge. For players who want to figure out for themselves who the traitor is, there are areas they should focus on.
Soma in Assassin's Creed Valhalla can be found in Grantebridgescire, luckily this mission is part of the main storyline meaning that whatever you do, you won't be able to ignore this mission.
Go to the top left of the island between Middeltun and the Deod River near the player marker and pointer in the image above. The boat will be there in a rather ragged state, as shown in the photo above.
While the reasons indicate it could be anyone, the real traitor is Galinn. Lif knows paint but knows how expensive it is to waste it. Birna says she is not bitter about Soma and has an alibi.