(spoilers for Silksong and Hollow Knight)
I have 100%ed both Hollow Knight and Silksong, and as I played throughout both games multiple times, I started to come up with a very unique take on the nature of Void.
Void is obviously one of the most important and mysterious elements in the Hollow Knight universe, a force that cannot be controlled or contained (if not for a limited time).
While never specified, Void seems to be at the very bottom of the world and not just under Pharloom or Hallownest, filling the entirety of the deepest sublayer of the "planet" in which the games take place, and every time it is encountered in game it is shown as a sort of evil destructive power that wants nothing but death and annihilation, but when we enter the Abyss of Pharloom we encounter 4 different creatures in it:
Shadow Creepers
Shadow Chargers
Gloomsacs
and Gargantgloom.
What make these creatures unique is the fact that they are ALIVE and have evolved specifically to survive in the environment of the Abyss. The way they act, unlike the voided husks in Pharloom, shows that they are NOT "controlled" by the Void, moreso they EVOLVED to survive in its environment and in close contact with it.
I know this may sound insane but, judging by the fact that (unless you actually get close to the Void itself or try to disturb it first) you can actually stay within the Abyss undisturbed, and the void will NEVER climb up to you by it's own volition (moreso, the Void climbs into Pharloom because Grand Mother Silk is doing her thing with the coccon in the Abyss and it's climbing the threads upward, unthinking of what it's doing), show that the void is much more calm than any Higher Being.
NOW HOLD UP! I know what you're thinking:
"More calm? It keeps killing everyone it comes into contact with!"
Yes, but, we have seen time and time again that the Void has never willingly attacked any kingdom DIRECTLY. The Void is a force/entity/conglomerate that WANTS to be left alone.
While it is said that Void has no will, I genuinely think that the Void has TWO desires: one is to BE LEFT ALONE, and the other...
...Is to feel alive again.
I believe that the Void is a very tragic entity actually, since I believe that the Void is the very fusion of all the previous dead bugs of the previous civilizations and kingdoms that existed over the centuries.
To explain why I need to explore the other 2 forces that govern the Hollow Knight universe:
Soul and Dreams.
. . .
Let's start with Soul:
This may sound very basic and a bit disappointing, but I GENUINELY believe that soul is NOT that deep of an element. My idea is that SOUL is just how the bugs of this universe call the hemolymph, the "blood of bugs", which takes the form of a white goop for most irl insects (sounds familiar?)
The idea of Soul being the in universe equivalent to hemolymph in my opinion makes the most sense, especially with it's description of it being what give life to all bugs. But unlike the real world in which we connect the two, I believe that in Hollow Knight, soul and consciousness are TWO separate things.
And that's when Dream (or Essence) come into play:
Since the "soul" is the equivalent to hemolymph (aka blood) then Essence is the equivalent to an "actual soul", a spirit that can linger after death.
This could imply that in the Hollow Knight universe, the realm of dreams is the equivalent to our afterlife, and even the existence of two different types of BASE essences (dream and nightmare) plays in the idea of HEAVEN and HELL.
Essence is the REAL SOUL of bugs, the memories and emotions and ideas of a bug, which can (like real life ghosts) get trapped in the living world and "haunt" an area if they have unfinished business, died in an horrible way or refused to accept their demise (as shown all throughout Hallownest, only for us to "free" them with our dream nail).
(just to clarify, the Silk Memories of Silksong are just MEMORIES, not ghosts, just memories trapped in time by Grand Mother Silk ever present strands of silk throughout the kingdom. Despite this, Silk is made of Soul (hemolymph,) so it can be used to create a FAKE CONSCIOUSNESS, as seen with Lace and Phantom, but it's not akin to ESSENCE, the REAL SOUL of bugs).
. . .
So, if SOUL is the blood and life energy of bugs, the basic power that keeps them alive, and ESSENCE is the ghosts of bugs that will pass on to the afterlife, what IS VOID?
Void is, like Confessor Jiji says, the REGRETS of bugs.
It's no wonder that the void looks like tar or oil, since it is most likely made of the decomposed bodies of bugs, seeping into the earth and depositing deep below the most ancient caverns.
The Void is the remains of a body lacking both SOUL and ESSENCE, the remains of a dead bug and the remnants of desires and will to live.
The Void has shown time and time again to do tons of very weird things: taking the shape of weird roads or structures, taking the shape of buildings even (as shown by the abyss spires and roads, including a description that talked about the rock itself bending itself to create roads and streets), becoming almost entirely docile when given a purpose which will follow to the very end (almost as if trying to feel contempt in fulfilling it), as if the Void was trying to recreate the life it had before but never being able to copy it perfectly, due to its lack of SOUL and ESSENCE to guide its judgment.
Now let's get back to the Void attacking the bugs of Pharloom but not the ones in the abyss.
Why does the void do that?
Simple: because the bugs that evolved to survive in the abyss are more akin to ANIMALS, without a real consciousness or "soul", they are animals driven by instincts, and thus the Void is NOT attracted to them. On the other hand, the bugs of Pharloom ARE PEOPLE, with a soul, with emotions, with LIFE and desires, EXACTLY WHAT THE VOID CRAVES FOR AND LACKS.
Void is not an entity that actively seeks to kill or destroy, it just stands still and drowns in its own misery and regrets, but when a bug with a SOUL AND EMOTIONS gets near, it gets desperate to enter inside them to feel alive again.
Which brings us to the final part: why is Void so obsessed with HIGHER BEINGS?
It's obvious: they are the prime source of CONSCIOUSNESS in the entire Hollow Knight world.
It is implied in the first game that the world of Hollow Knight is made up of mostly animalistic bugs with no consciousness or "SOUL", and the primary reason why they develop such things is thanks to Higher Beings that decide to give them an intellect, a mind and a personality.
This leads to a very disturbing idea:
Void is most likely born BECAUSE Higher Beings started to create civilizations.
Before, when bugs had no mind or soul or desires, they would simply die and cease to exist, decompose and... that's it
But then the GODS started to give bugs ideas and minds, ONLY THEN, after death, the Void was born, from the regrets of those intelligent bugs, after all:
Regrets can't exist if you don't have a mind to understand what they are in the first place.
This is why the Void CRAVES to kill Higher Beings: both to absorb their energy in an attempt to feel whole again, and to PUNISH THEM for giving birth to it, for condemning it to an existence of emptiness and regrets.
This is what the Void wants, its true objective.