Horror (?) movie with prisoners who try to survive by being “statues”

Hi guys! I want to find the title of a movie that my sister described to me. There are a lot of chances that this movie is relatively new because it seems like everyone is watching it right now.
All that I know is that there are some kind of prisoners wearing blue uniforms and that there are also their guards who wear masks with geometric shapes (square, triangle, circle etc.). The prisoners must cross a line and at the end of the “arena” there is a giant doll with cameras for eyes. When the doll turns their head the prisoners must stay still otherwise they die. Moreover, I’ve been told that there is a grandpa who has survived and he is an expert at this “game”.