Comment by hamdingers

Odd if true. It's clearly a universal binary, not sure what's going wrong for you.

$ file steam_osx

steam_osx: Mach-O universal binary with 2 architectures: [x86_64:Mach-O 64-bit executable x86_64] [arm64]

steam_osx (for architecture x86_64): Mach-O 64-bit executable x86_64

steam_osx (for architecture arm64): Mach-O 64-bit executable arm64