The way you get shoulder-aimed kills in Sniper Elite 5 differs from Sniper Elite 4. Even though the game doesn't explain how to use the feature, it's impossible to forget once you learn how.
How to aim from the shoulder in Sniper Elite 5
When you aim regularly, you will aim through your scope. Aim as you normally would and press A (Xbox) or X (PlayStation) to toggle how you aim. This will switch you from a scoped aim to an over-the-shoulder perspective.
It's a lot more challenging than using the regular scope, but it's more of a third-person shooting method. You can change the aiming method of your pistol and SMG the same way, except they switch from third to first-person aiming. While you can switch back and forth as much as you like, make sure that you are able to shoot in that view.
Players should only attempt to aim without a scope when they have a sniper rifle that is meant for close-up shots. Many targets will be very far away from the player, but some will be close enough for over the shoulder aiming. This aiming style allows you to adjust your aim faster and increases your FOV for close-up engagements.
For more on Sniper Elite 5, check out Can you disable Axis Invasion in Sniper Elite 5? or How many missions are there in Sniper Elite 5? Complete Mission List here on Pro Game Guides!