My character believes and accepts the fact that there are multiple deities responsible for creating and influencing the world. She acknowledges their existence, powers, capabilities, and the like, but she doesn’t worship or pledge allegiance to any one of them in particular.
Is there a commonly accepted term for this belief system? Seems close to agnostic, but this doesn’t seem just right. Maybe something like ‘pantheistic’?
Theism & gnosticism are completely different things.
In general English language usage, theism is about belief in the divine, so a theist believes in the divine while an atheist does not. Gnosticism is about the ability to know the divine, so a gnostic believes we can empirically know about the divine the same way that we know that 2+2=4 or that bananas are yellow, while an agnostic believes that we cannot empirically examine the divine, and must relate to it through belief only.
In a D&D setting your character is almost certainly a gnostic polytheist, someone who believes that multiple deities exist and that that their existence can be examined empirically (since divine magic is a thing), even if she doesn't actively worship any particular deity. Pretty much everyone in a standard D&D setting is a gnostic polytheist; D&D languages likely don't even have words for what we would call atheism or agnosticism.
If your character actively opposes worship of gods (any god, not just specific gods) that's called atheism in D&D even though it doesn't match the general English-language definition of atheism. That doesn't sound like what you were describing, though.
Your character is a polytheist, someone who believes in the existence of multiple gods. Polytheists do not have to worship these gods.
Pantheism is the belief that all reality is identical with divinity, or God is everything. It doesn't fit what you propose.
Agnosticism is the view that the existence of God, of the divine or the supernatural is unknown or unknowable. It also doesn't fit your definition.
Here is an attempt for an in-game answer.
Within the D&D game, the closest in-game concept that closely mirrors your description is the philosophical position of the planar faction known as the "Athar". The in-game word for members of this philosophical club is Defier. The term originated during the 1990s (AD&D 2e) with the Planescape campaign setting. The faction was also updated to D&D 3/3.5e in articles published in the Dragon magazine.
Once a character travels to the Outer Planes, part of the core cosmology of the D&D game (also known as the Great Wheel Cosmology), it becomes quite clear that deities are super-powerful beings. Members of Athar accepts their presence, but sees them simply as powerful beings and not worthy of worship. Some militant defiers will actively try to undermine religious orders, while others will simply ignore them. So your character would just be such a "soft" defier.
Another in-game word that is used in the Forgotten Realms setting is Faithless. In the polytheistic Realms, everybody worships all the deities, with one, a so-called patron deity, given the most importance. If you do not worship any powers at all, you are said to be faithless.
However, please note that there are some consequences. If priests learn that your character is a defier, they are likely to refrain from using their beneficial spells on you. And on Faerun, if you die faithless, you end up as a brick in a wall in Kelemvor's realm for the rest of eternity.
