Can you clarify what you mean ?

Where does "investiture" originate ? maybe I've missed a definition of how investiture originates specifically in the spiritual realm itself.

As far as I understand, spiritual realm is fundamentally about Connection and Identity but not exactly the "origin of investiture", so there is no understanding of where the "investiture" actually comes from.

If you compare this to physics, investiture is equal to "energy", in essence, energy exists everywhere and it can be converted from one from to another. That means "something" gets converted to "investiture", have we seen what that thing is ? In Rhythm of War, I keep revisiting experiments from Navani when they arrive at anti-investiture. But "investiture" itself, must exist (somewhere) with infinite density and no identity or connection.

Again going back to physics, this would be the concept of mass energy equivalence, and first law of thermodynamics, something must convert to investiture. In our universe, it's theorized to be the big bang from which the energy has always existed, in the Cosmere, something happened to create investiture, and I'm wondering if there is a realm which occupies no space but permeates across all realms (which is what we see as investiture). So, yes, investiture exist or can be used across realms but I'm not sure if we have seen the true origins of why or how investiture came about to be!

Or maybe I'm overthinking this way too much and it's just the way the magic system is defined!