This comment in the README reads like it is not currently working, but I would suggest you to ask people involved in the box86/64 projects or check if someone in the RPi community has managed to do it: GitHub - ptitSeb/box64: Box64 - Linux Userspace x86_64 Emulator with a twist, targeted at ARM64 Linux devices
Edit: This reads like 32-bit Steam is somewhat possible GitHub - ptitSeb/box86: Box86 - Linux Userspace x86 Emulator with a twist, targeted at ARM Linux devices