Currently, quest markers can be only turned off on the map, but even if you do, they still appear on the compass and directly in the world - even if the quest isn’t set to being tracked. Also, to turn them off on the map, you have to choose only ONE set of features to see, and you can never see the names of geographical features (e.g. “Södra Salholmen”) that way.
I feel like the game is really shooting itself in the foot here. You have all these cool quest descriptions and items that giving hints enough hints to find the objective if you use your brain… and then drop a giant spoiler in the form of a quest marker right into the middle of the HUD.
Now, I get that a lot of players don’t want to do the scavenger hunt and just want to get to the shooting (and/or looting) part. But for those that do, it would be really nice to have more control over if, when and where quest markers appear.
Easiest fix would be a global setting in the Game options. A bit more work but better would be a sub-menu in the quest log for each individual quest, where you can set whether markers for that quest appear in the world, on the compass and on the map.
Addendum:
I’m only talking about the blue and orange objective markers here, not the “magnification glass” markers for quest items. For the latter, it might be nice to (again, optionally) make them a bit more vague - e.g. appearing over a house containing the hint/item, instead of directly on the item.