[Demon] [2008-2018] Game about a demon(not sure)

I'm looking for a realistic, modern-setting game (pre-2018).
You start as a human alone on empty streets, using a pistol against zombie-like enemies.
Key story moment: After progressing, you meet a powerful being who mocks you for trying to use guns against him (something like "You think bullets can hurt me?"). He then personally grants you the power to transform into a demon.
Gameplay after: The demon form is a key ability, used mostly for solving physics puzzles — like moving heavy crates and rotating large stone wheels (like millstones).
Specific scene I remember: There's a puzzle in an auditorium or large hall. Under the podium/stage, there's a hidden switch that opens a secret room. Inside that room, you need to move/interact with millstone-like objects to solve it.
Other: The camera view might be switchable. The game could be downloaded from non-Steam platforms.
Please help! This is very specific.