Set the last statue | Thanos Gorecki & Aurum Runes The Sexy Brutale Guide

Before you interact with the last statue, you have to wait for Aurum Runes to do it. Enter the room shown in the picture above and hide in the wardrobe.

Around 7:20 Aurum will enter the room. Wait for him to rearrange the position of the arm, and when he leaves the chamber set it to the correct position. This should start the cutscene that concludes this stage. Provided, of course, that you have completed all tasks correctly.