Apple's fat binaries were never very "universal". They put in a codepath where macOS detects and handles macOS-arm-and-x86_64 binaries. That is something where

Apple's fat binaries were never very "universal". They put in a codepath where macOS detects and handles macOS-arm-and-x86_64 binaries. That is something where they can support both variants, and themselves in control. Cosmopolitan libc is a pile of hacks, compared to that, more comparable to somebody making Linux boot on a 4004 CPU than what Apple did.