The -S / --split-string option[1] of /usr/bin/env is a relatively recent addition to GNU Coreutils. It's available starting from GNU Coreutils 8.30[2], released on 2018-07-01.
Beware of portability: it relies on a non-standard behavior from some operating systems. It only works on OSs that treat all the text after the first space as argument(s) to the shebanged executable; rather than just treating the whole string as an executable path (that can happen to contain spaces).
Fortunately this non-standard behavior is more the norm than the exception: it works at least on modern GNU/Linux, BSDs, and macOS.
Not to be negative, but is this warning of non-standardness for like, AT&T unix or something? Beyond Linux, macos, and BSDs, I'm assuming you're running an ancient mainframe or something and are not worried about trying a cool docker shebang hack (probably because docker doesn't exist on your platform anyway)
Beware of portability: it relies on a non-standard behavior from some operating systems. It only works on OSs that treat all the text after the first space as argument(s) to the shebanged executable; rather than just treating the whole string as an executable path (that can happen to contain spaces).
Fortunately this non-standard behavior is more the norm than the exception: it works at least on modern GNU/Linux, BSDs, and macOS.
[1] https://www.gnu.org/software/coreutils/manual/html_node/env-...
[2] https://github.com/coreutils/coreutils/blob/b09dc6306e7affaf...