It's not a casual thought. I recognize that there are lots of details, there always are, we're talking about computers :)

Linux posix_spawn is a wrapper around clone and exec. There is no primitive on Linux to create an entirely blank process. This is adequately discussed in the linked LWN post.

Other operating systems either have parallel APIs to fork (e.g. the posix_spawn syscall on macOS) or do not provide fork at all (Windows).