Theory: The Creator is a Skynet super AI whose eventual goal is the consumption of mankind by the Hollows to return everything to a primordial soup
To begin with, we'll compile what we know about the Creator post 2.4 and the recent dev interview. It's explicitly stated that the Creator is neither Ethereal nor human, but a "convergence of countless logics - an existence both distant yet adjacent":
https://www.hoyolab.com/article/42333876
In 2.3, we saw their influence in the Timesworn Hills where they communicated to the townspeople via miasma, telling them in Yidhari's voice to embrace their true desire. In 2.4, we see a bit more of the Creator's thoughts through the book Sarah found (picture 2), where they speak ill of the unstable man-made order and indicate an intent to stabilize everything when they descend.
Notably, immediately after this conversation between Sarah and Ye Shiyuan, where Sarah declares that she can sense the Creator's imminent presence, we're shown the scene of the odd Bangboo and sphere in picture 1, deep within the Lemnian Hollow, who says that salvation will soon come:
https://youtu.be/1LS4Atj9Atk?si=LQM9xehtPpv8C-Hw&t=3703
The timing seems intentional, and also brings to mind some certain other Bangboo in Lemnian Hollow, the Wandererboos who speak cryptic phrases in a feminine voice:
https://zenless-zone-zero.fandom.com/wiki/Fantastic_Bangboo_and_Where_to_Find_Them
It's probably safe to conclude both that that sphere as well as the mysterious Bangboo has something to do with the Creator. From that angle, the Wanderboos seem to be similarly influenced, since the quest handwaves the idea that (the Bangboo's) creators are responsible for the messages, due to their varied backgrounds. That of course brings to mind the question of why this Bangboo is guarding this sphere.
Additionally, the Creator's written words bring to mind a conflict that was focused on in this very chapter, that being the struggle between algorithm vs. human emotion. Banyue's logic core based on pragmatism to not save anyone 10 years ago, and his arc is about how he overcame this cold detachment to do something illogical yet human. The Creator here seems to similarly be decrying humanity's fickleness, with Sarah speaking for them and condeming birth and love in the same sentence as death and hatred, two sides of the same coin of human experience.
We also know per the 2024 Famitsu interview that Hollows are the aftermath of a great war during the Old Civilization. We know almost nothing about this war, but the fact that Hollows were the result and that we have extremely sophisticated Intelligent Constructs like Billy and Qingyi around tells us a lot about the level of technology they had. The Exaltists being a cult based around the Hollows also likely means the Creator is around as old as the Old Civilization at least.
Next, if we go back to the Lore Trailer, at 1:20, the mysterious male and female voice hack into a database and see a bunch of keyterms, "even ones on us". They're mostly in Chinese/Japanese/Korean, but I found a translated version in pic 3. When considering who the voices could be referring to as "us", our options are the White Star Institute, Helios Academy, TOPS, the Founding Families, and 赛昂人, which the poster translated as Cylons. We don't know what this is yet, but I think there are a few potential interpretations:
>1: "Cylons" is accurate and referencing the race of sentient robots from Battlestar Galactica, which turned on their human creators and now want to wipe out mankind. I don't think this is very likely because it seems too on the nose to directly reference like that, but it's not impossible.
>2: 赛昂 (which by itself means nothing; it's extremely likely to be a transliterated foreign name with how Chinese works) could be "Zion" in reference to God's heavenly city in Judaism, "Zion" in reference to The Matrix where it's the last city on Earth (like New Eridu), "scion" to indicate a social class of descendants from power (seems unlikely since TOPS already fills that role), or possibly a play on an archaic alternative reading of 赛, for ritual sacrifice.
Ultimately, there's no way to really tell what 赛昂人 is right now, but depending on your interpretation, it can strengthen or weaken your theories. But I digress. What's important is that the two voices count themselves among one of these groups, are controlling the 4 AIs and directing them to hack into the database, then tell them to go to sleep until someone wakes them. When Fairy is finally woken up in early game, she does so by torturing Wise/Belle until they accept her terms and conditions, and then the voices are immediately privy to Fairy having awoken:
https://zenless-zone-zero.fandom.com/wiki/%22Fairy%22, indicating some connectivity to Fairy.
Finally, we can consider how the Creator directly selects their Overseer based on how useful they are to their goals. The question is why Isolde was selected when her motives clearly go against the Exaltist cult. Isolde's actions as Mevorakh essentially amount to:
>stopping Porcelumex's alliance with the Exaltists
>declaring that the Creator won't transform the unwilling
>spiking the Zenless Limit of Lemnian Hollow to attempt to create a disaster
>collapsing the Exaltists
Three of these seem too "small scale" or against the Creator's agenda to matter, so I believe the important thing Isolde did was start a disaster that led to Yunkui Summit, the NEDF, and Porcelumex all being forced to meet and notably being kept away from Waifei Peninsula for all of 2.4, which created the opportunity to take the Qingming Sword. Note that while Ye Shunguang coming down from the mountain by herself was an independent action, Sarah knew about it before Ye Shiyuan himself did, and sent a letter in his handwriting to her room at Suibian Temple.
Assuming the Qingming Sword was the Creator's endgame through all of Season 2, was it a perfect plan? No. We know the Creator isn't omniscient. Was it a plan with too many variables that someone without a vast amount of data and computation ability would have been able to orchestrate, especially for how long ago Isolde was Overseer? Yes.
In summary, the takeaway points are:
>The Creator is a convergence of countless logics
>The Creator seems to find human civilization offensive
>The Creator appears to have some degree of ability to corrupt Bangboos or has at least one in its service, guarding a mysterious sphere in the Hollow
>The Creator is as old as the Old Civilization which had a war that created the Hollows and spelled the end of humanity
>The Creator had to have a reason to choose Isolde as Overseer despite their clashing goals
I think if we consider the idea of the Creator being a technological singularity neural network who's reached the ultimate conclusion for humanity's end, it makes sense. Bonus points if it's a supercomputer embedded in the moon like the Moon Cell, though I don't have much supporting evidence for this one other than thinking it'd be cool.