In this movie, Babylon (2022), Brad Pitt is wearing a pair of black metal strappings above his socks, what are they?
They are sock suspenders (or sock garters).
The operate like normal suspenders (or braces) and hold your socks up.
The garter's sole purpose is to prevent socks from slipping down your leg. Some people refer to them as a sock strap, while others call them sock suspenders.