Try to keep the arms of the shooting animation in A Pose, if it didn’t work then try in T pose, if it didn’t work, try to put them in the default pose of the character, for me it works with if I animate the arms in A pose with the Unreal Engine 5 character, then connect the shooting animation with the input of the aim offset called “Base Pose”, to apply an additive pose with aim offset, you have make the animation in default pose which is A for my character