What exactly is the difference between Shinjutsu and something like Gaara’s sand?
I'm not sure what people don't understand, it's pretty straightforward.
Ninjutsu requires handseals and concentration of chakra.
Divine arts are "miracles" carried out as casually as breathing.
If Kirin could be executed by casually twitching a finger and nothing more then it would fall under the category of shinjutsu.
Code can open portals to literally anywhere in the planet and any dimension by simply swiping a finger.
No concentration, no hand seals, no chakra strain etc
It's not just about how impressive it is, but how such a feat is executed.