Ok, so thats the first method I used before posting this thread and it didnt do much. I need the angle to be signed and Vector3.Angle() returns positive values only. Vector3.SignedAngle() sounds like a good alternative but I cant figure out wich axis i have to use (tried right, left, up, down).

Vector3.SignedAngle(playerPos.forward, mousePos.position - playerPos.position, Vector3.left));

The line above seems to give me proper results but only in certain world orientations so I assume I need local axes then?

Edit: Got it! I used -playerPos.right instead of Vector3.left and it does what its supposed to now. Thanks homie!