Long story short. As long as your feet do not move for a couple of seconds you are 100% invisible on all available in game settings.
They can still see your arrows when you shoot, the red line target when you use the shoulder cannon, etc. You yourself are invisible.
There are of course ways to find you and many players are scary good at it. Example if they guess and fire a few shots they will get the X hit indicator if a bullet hits you even if you are invisible. Then it stands to reason they can continue to hit you by shotting the same place again.