'In the Earth Under the Forest' is a day-in-the-life, fantasy-adjacent, vignette that exemplifies values such as emotional awareness, conflict resolutions, and communications. It makes great use of all the various community sprites, and all of their unique quirkiness to weave a story with just as many unique and fantastical details of this 'fae-like' forest setting. This story really does act as one half 'dealing with relationship conflicts' and one half 'nature documentary'. The romance is sweet and simple, and is surprisingly not the focus of this story.
This story is very character-driven, with each of the characters showing off their personality though dialog with each other, though some I felt were more successfully communicated than others. The one through line that I noticed is that everyone was overbearingly socially polite. I don't think that's particularly a bad thing to showcase social politeness like asking pronouns, permission to hug someone, or using almost clinical level of mental check ins, but scenes do seem to be artificially inflated each time that the inner monologue brought attention to these social graces. With all the characters being different hybrids of species, I don't think I ever got a clear visual on what the main character was or looked like, only gleaming that they were a cat of some kind by context clues later in the story.
My biggest issue that I can find in this story, is that the characters don't seem to have any flaws, or the flaws they have are so minor and easily resolved that there's not much of a big payoff at the end. Throughout the story, the only conflicts are 'you can't move to the forest because reasons' and 'something is wrong with the forest because reasons', so it doesn't feel like any of the characters have an arc, grow, or learn something once the reason is uncovered. Some examples I could think of would be making the mother be actively showing her disdain against outsiders, have the friend have a visible jealousy streak of you, giving the wolf partner an anger issue and inability to vocalize his feelings, etc. Giving characters flaws is what allows them to have a starting point to grow from.
The overarching theme of this story seems to be about listening and communicating effectively, which is why I think it makes sense the final solution to the story is 'listening to the spirits under the forest', but the story needed to build up to it better. Something that we discover can only be done by a 'special person chosen by the forest', which is a concept introduced much later and bestowed upon the main character 'chosen-one-style', also kind of undermines the idea that everyone should be able to listen. One consideration is to up the amount of family disputes earlier on in the story, to parallel the idea that conflict is what happens when people talk past each other, and resolving it is to get over yourself and start listening.
As far as 'light in the dark' themes, I think it's the glowing mushrooms in the earth that is supposed to be the light in the dark? Figuratively, it'd be a stretch to say that the emotional or metaphorical representation is the main character being a 'light' to contrast with the 'dark' of... the forest injuring it's inhabitants, so I feel this story didn't quite hit the brief. The romance aspect of this story is very light and sweet, surprisingly easy that this couple turned into a throuple in three days. Overall, it's a very creative setting and the use of the sprites, and the story is a pleasant read, if a bit one-note. I commend you on the word count, however, shows that you're capable of doing the writing, just need to hone in on refining it.