From Wikipedia:
Light spots and shadows
https://en.wikipedia.org/wiki/Faster-than-light
Of course, the shadow must already be cast, in a continuous stream of uniquitous photons, which all need to be arriving upon the reflective surface at the speed of light, before the shadow can transit the surface within the area of effect.
At best, only the destruction of matter can move at the speed of light, so a reduction of gravity may propagate, as fast as the dispersal of the dematerialization and subsequent radiation.
Accumulation of mass as a knock-on pile-up of massive particles would need to be studied, to assess how quickly the shadow of newly created matter can induce its respective gravitational phenomenon. Figure star nurseries and supernovae events (and similar generative or cataclysmic reactions) would be the place to look. LIGO studies try to do exactly that, but the investigators seem to relish conflating an interpretation that favors signal transmission, and thus "particle/wave duality" because math.
Gravity-as-a-wave, meanwhile would be sort of like an illusory sound-as-a-wave being a byproduct of kinetic energy in a material aggregate serving as a bystander medium of propagation. Sound is not it's own "force" although we can readily recognize the phenomenon as a principle that behaves with similar attributes, parameters and effects as observed elsewhere, in other fundamental systems.
That LIGO instruments can detect gravitational influence in one part of the apparatus, before the other part of the apparatus registers the phenomenon, is really not unlike saying dominos demonstrate gravitational waves, because toppling the first domino does not topple the last domino instantaneously.
That photons can be influenced by a side-effect of material accumulation, bending or altering their path of travel probably says something about the photon or the environment being travelled through, more than it does about space and time.
But the environment they travel through is space and time.
Semantic in the sense that the word "environment" is a loaded term.
I'll offer this much: photons are particles. As particles, we know them to be part-time resident constituents of massive objects. That massive objects are representative of large quantities of energy trapped and oscillating in bounded standing waveforms.
We know that the empty vacuum of space really is mostly void, but also that a lot of photons (particles) are still traversing the void quite a bit.
So, space/time, while an empty void, where phenomena transit or conduct themselves theough said empty medium, is still an environment with varying concentrations of activity.
If an neutron manages to be ejected from a supernova, and is directed toward our solar syatem, and is influenced to fall toward the sun, but, miraculously passes straight through the sun, without colliding with any other particles, only to travel onward toward the center of the galaxy, landing in a supermassive black hole some millennia from now, what would you say about the environment this neutron experienced as it fortuitously passed through the center of the sun, without experiencing any collisions?
Would to rob it of all the other qualities, and just label it space and time? Or would you refer to it as an environment, with activity transpiring, in addition to be also being a realm of space and time?
Photons are also waves in the EM field.
> As particles, we know them to be part-time resident constituents of massive objects.
I don't think you can say we know that without explain what that means. In no part of physics do we discuss part-time resident constituents.
Your comments use a lot of terms that seem to be of your own creation. Unfortunately, these terms make it hard for your points to be understood because they lack the shared naming conventions that the field of physics uses to discuss these phenomena. Standard naming conventions, both in programming and physics, are enormously important in conveying ideas between people.
The whole point of the paper is studying the effect of gravity on gravitational self-energy, i.e. NOT matter. You'll find no "matter term" in Einstein's equations.
In the observable universe (regardless of theories and expressions penned on paper) gravitational forces are always induced by massive material objects, including the remnant artifacts of deceased stars. To suggest otherwise is to walrus the conversation.
Being a theoretical hypothesis, formed to explain observations, it remains a side-effect of accounting and inference, and has not been located directly.
Show me why you believe it is a thing. Show me where you have found it. Tell me why it isn't actually matter.
But then gravity changes would be felt instantaneously rather than propagating at the speed of light.