The encounter against Steiner is not like a traditional boss fight as it is more of a test of patience. It is all a game of hide and seek. Throughout the fight, the player must not get discovered. In this Call of Duty: Vanguard guide, we have detailed all there is to know about how to beat Steiner.
Call of Duty: Vanguard Steiner
Before we begin, do note that there is no point in taking on his head-on. Once the encounter begins, try to avoid his line-of-sight and creep up behind him for a quick melee by pressing R3.
Once the cutscene ends, turn off the gramophone and begin the sequence once more. Use the nearby crawl-spaces to break the line-of-sight once more but do not remain there for too long. Once the line-of-sight breaks, once again, sneak past him and press R3 to deal a massive amount of damage.
Following that, the player will need to do that once again i.e., sneak behind Steiner and stab him. Again, a cutscene will begin showing Steiner making a run for it at the rooftop. Now all that remains is to follow the blood to the rooftop and watch Petrova kick him off the roof.
This is all we have got in how to beat Steiner in Call of Duty: Vanguard. For more help on the game, be sure to check out our detailed Call of Duty: Vanguard wiki page.