The Elden Ring must be housed within darkness
I posit this theory based solely on in-game evidence. I will reference established themes of duality, in game content (cutscenes, environmental assets, item descriptions) only, without looking to translation descrepencies or IRL mythology. But hopefully you'll forgive my Kabbalist plug at the end, as I feel it matches the ER creation story almost 1:1 (even speaking of a "Divine Will"). Anywho...
The first time we see the Elden Ring (ER) is in two cut-scenes/videos. I can't remember if this was the launch trailer or something, but in one of the promo videos (can't link YT videos), we see Marika and Radagon playing whack-a-mole on the Elden Ring in complete darkness. We also see this in the opening cinematic, albeit a different artstyle. The screen fades to black, only re-appearing when the ER is struck. We then see this AGAIN when we walk into the Erdtree ourselves later in-game. Though we can see inside, I'm pretty sure this is...you know.. so we as the player can see what's going on.
Before we enter the Erdtree though, we enter Farum Azula. There is a unique depiction of the Elden Ring here, glowing with a divine light (non-static asset, has particle effects). It's literally glowing with divine energy. I'm not saying it's the ER, but it's distinct compared to the ER depiction on the ground where we fight the Grafted Scion outside the Chapel of Anticipation. What's more interesting, is that the temple which houses this depiction used to be in complete darkness before FA was damaged. This further creates this connection of darkness with the ER. Beastmen and Maliketh are seemingly blind, wearing things that cover their eyes and having grey/white eyes on their character models.
Lastly, when we finally see Radagon in the flesh, aside from being in a dark place where the ER is housed... he contains the ER within a Shadowy miasma. The Elden Beast, a living embodiment of the ER, emerges from shadow as well. The Elden Beast itself is darkness containing veins of light. Radagon is intrinsically connected to shadow/darkness via thorns. He commands thorns that bar us entry from the Erdtree, with Melina referring to a "mantle of thorns" (the only other time this phrase is used is in the DLC thorn spells, found in a "Shadow" keep). Enir-Ilim is also covered in... shadow thorns.
Stars and divinity are intertwined narratively in this game, and stars exist within the darkness of space. Even the Greater Will, postulated as this golden divinity in base game, is revealed to be a "lightless abyss" in the DLC. Quite converse to the "One Great" postulated as this original divine light. I could expand on this way more, how it mirrors the creation story of Jewish Mysticism (specifically the Zohar) almost 1:1... but I won't. On a fundamental level though, darkness can only exist if light is restricted. The Greater Will was the One Great's self-realization. To have anything other than it's infinte divine light, it had to create distinction: the first darkness... the Greater Will. One cannot exist without the other. Note how the Greater Will "sent" Astel;s, and they are anything but "shining" or "golden". They come and disappear from voids. Metyr, equally grotesque, commands similar voids/black holes. The Greater Will's "lightless abyss"... The One Great/Greater Will, dual aspects...you just gotta choose: do you worship the gold font of existence? Or the dark, intelligent choice that spawned us all? OK I'm done with this part, because I know we'll all have varying takes on the One Great/Greater Will.
I think the point I'm trying to make is that duality is the central theme of this game. Light and Dark are two sides of the same coin (darkness simply being the absense of light/shadow cast by it, depending on how you interpret it). We have proof that this dichotomy exists in game explicitly via the Sword's of Light and Darkness. I find it interesting then, that when we DO see the Elden Ring, the embodiment of light/gold, darkness accompanies it.