This is a unit package that works

My-Fourth-Modules-Script.pm6

#!/usr/bin/env perl6

unit package My-Fourth-Modules-Script;

our proto MAIN($) is export { * }

multi MAIN($x) {
  say "This is the inside MAIN called with $x";
}

# No output:
# $ ./My-Fourth-Modules-Script.pm6
# $ ./My-Fourth-Modules-Script.pm6 242
# But, run correctly:
# $ perl6 -M My-Fourth-Modules-Script -e ' '
# Usage:
#   -e '...' <x>
# $ perl6 -M My-Fourth-Modules-Script -e ' ' 32
# This is the inside MAIN called with 32