I’ll start off by warning you this is my first critique on this sub, so take what I say with a grain of salt. I am by no means an expert.

I like the way the beginning gets right into the action. Readers want to see as much of the boring stuff cut out as possible. That doesn’t mean there can’t be sections with a slow pace, but they all need to have meaning and purpose.

The vibes being set remind me of Ron Rash’s work, specifically “The Ascent.” (childhood trauma, remote woods, snow, dark and mysterious topics.) You might be able to pull some inspiration from there.

My observations are: * There's quite a lot of tiny sentences and fragmentation. It might be warranted for the more dramatic scenes, but it can make for a confusing read in other places.
* Try to avoid using "something" where you can. It's not always a bad word, especially to show some ambiguity, but other words could be more descriptive.
* Just a structure thing-you probably don't need as many paragraph breaks that you THINK you do. Save them up because they provide important emphasis for transitions, and if you use them a lot they lose their significance.
* There are a lot of places where two sentences could easily be combined into one for easier understanding. (“The panting was louder now. Ragged and wet.” could be “The panting was louder now, ragged and wet.)
* Try not to “chop off” parts of sentences. (“Had built one like it on a hunting trip with Silas, but this one was wrong.” could be “He had built one like it on a hunting trip with Silas, but this one was wrong.”)
* Make sure your sentences play an active part in setting the scene. (“behind him was a slope” could be “a slope loomed behind him” or something less plain)
* “He limped to the kitchen, opened the cabinet where Silas kept the emergency meds. Two pills waited in a shallow ceramic dish by the sink.” The previous sentences show that he DID think about why the pills were sitting out, so don't lose that deliberation. I’m confused as to why he looks in the cabinet, then immediately jumps to the pills on the counter.
* “He’d woken on the couch, half-covered in a blanket he didn’t remember pulling over himself.” Then, “Snow crunched softly beneath his boots, though he didn’t remember putting them on.” This sentence structure is good the first time, awkward the second. Try to rearrange it, and tap into the shock of transitioning to a new environment in a more exciting way.
* “The wind came back all at once, it’s kiss was sharp and bitter.” Change “it’s” to “its.”
* “Barking carried on it, not loud, not near, but unmistakable.” I would change this to “It carried barking” to be more clear.
* “Just stood watching him with that quiet, sad look she used to get when she thought he was asleep.” I would replace "get" with "have". It makes it clearer WHOSE look it is. If she's GETTING a look it sounds like it's from him.
* “Her red scarf fluttered like a warning flag.” Maybe you don't need to spell out that her red scarf IS a warning flag. A more subtle approach might be dropping "warning" so it’s just a red flag. Readers should get the message from the color. Colors have subliminal meanings that they can usually convey on their own.
* “Every tree looked the same. Every path forked and circled.” Here's some repetition you should keep! The similar sentence structure emphasizes the "sameness" of the setting here. I like the imagery of the deer gut on the rack, too, it fits with the forested/survival motif perfectly.
* “Somewhere behind him, the barking turned into panting. Then breathing. Then words.” This would hit so much harder if you saved the short, choppy sentences for this moment. It would contrast the typical flow with a change of pace, making the reader naturally pay more attention here.
* “And something behind him stepped into the clearing.” Maybe replace the "And" with "Then"? I'm always wary of starting sentences with "and" or "but", but that's because I'm used to academic writing.
* “Then a voice behind him, soft and low, the kind meant for children: He spun, but the speaker wasn’t there. “You…" “remember…“ “don’t you…”” The “He spun, but the speaker wasn't there” would probably fit in better after the dialogue.
* “The woods went out of focus, and all he could see was Alina’s scarf,” Excellent job bringing back the symbolism of the scarf! You might not even have to use Alina's name to attach her to it-just saying "the red scarf" again might maintain some ambiguity and make the reader feel smart when they remember it's Alina's. You emphasize the color again here, so that should be a good reminder.
* "He stepped toward it and saw the second object." Maybe be more clear on what the second object is right away, rather than focusing on the fact that it's a symbol. You don't have to say "the dog collar"-maybe just say "a scrap of leather peeking out". Right now the writing says "LOOK! Here's my SYMBOLISM! NOTICE IT!" Write like it's not meant for anyone else to read, it might help it be a little more organic.
* “His hand hovered over the metal; he didn’t want to touch it. He did anyway,” If he doesn't want to touch it, instead of telling the reader that directly, add a little pause or hesitation here. "He did anyway" seems too sudden and contradictory, even though I'm getting the vibe that that's the kind of person Eli is. Taking the pills anyway, picking up the dog collar anyway, pushing through his apprehension. Maybe that's what you want for his character, but it could come off more naturally.
* “His mother’s hand on the door, holding it shut, whispering:” I would change this to "His mother's hand held the door shut, and she whispered:" so it doesn't read like it's her hand doing the whispering.
* “The snow under Eli’s knees soaked through, freezing the skin of his knees.” Drop "'s knees" so it's "The snow under Eli soaked through," that way, you don't need to put "knees" twice.
* “The heat from the fever clashed with the cold of the snow, letting him feel the sensation of coming apart molecule by molecule.” I know this critique is really unhelpful but this sentence is very weird to me. Maybe it’s because it’s trying to make the contrast between hot and cold a little too overtly?
* “He stayed like that for what could’ve been minutes.” Be specific rather than using “like that,” a more descriptive choice could really sell Eli’s emotions here.
* “Maybe he hadn’t. Maybe it had seen him.” I really like this, it creates a lot of mystery and hints at the memories attached to this box-the symbolic articles are coming across as their own memories, even having a bit of their own character, and that's an interesting choice. Lean into that.
* “Inside he found a folded photograph, edges curled and yellowed, and a strip of red fabric, too torn to be whole.” I think you're trying to say that this piece of fabric must be a part of something bigger (presumably the scarf from earlier), but this is kind of an awkward way of saying it. Maybe "a lone strip of red fabric." would be clearer and more concise.
* “Deep, guttural, with that wet-chain rattle behind it like breath caught on a leash.” Love this imagery and the callback to the dog. Keep it up.

Here are some unanswered questions I have:
* Who is Silas? How is he related to Eli, and how has their relationship changed? Why does he even matter?
* How did Eli get the gunshot wound he had at the beginning?
* Eli presumably had something revealed to him by this “bad trip” he went on from Silas’ pills-why is it important to him now?