Afaik cosmopolitan is only meaningful for executable startups, the actual x86 binaries can be platform-agnostic, but only if they basically do no communication

Afaik cosmopolitan is only meaningful for executable startups, the actual x86 binaries can be platform-agnostic, but only if they basically do no communication with the outside world (or very little), since otherwise they have to use OS APIs. So, not sure that the same version can be linked, but most libraries have a shared API with platform-specific implementations and one can just link against them, pretty much how it is done today in e.g. Blender. GraalVM is a bit trickier as it can be used to interpret LLVM bytecode, which will be portable across OSs, both when native compiled or when used on top of JVM. But if it uses Panama it would get the aforementioned limitations as it is basically just a wrapper over dynamically wrapping libs.