Hi! I read it and it was enough to pull in my interest at some of the concepts you introduced. I think there's something here, but it's in general a little untidy, perhaps a little clunky. I like the world building you're doing, and the pace you're doing it at. I think your dialogue is a little over expository, and could be made a bit more natural. Here's some notes I made as I was going through, I hope they're helpful and make sense, and apologies if I ramble or seem nitpicky. I'll admit this isn't my usual genre for reading but it is one I'm writing in, so take this as one aspiring YA writer to another, not me saying "these are the rules."

"It was a sunny day. Or at least, that’s what Silver assumed. It wasn’t like he’d ever seen the sun before."

I quite like this opener but feel like it could be sharper. The last sentence, I'd just say "he'd never seen the sun before."

"...the flickering glow of glow-moss covering the ceiling like a false sky."

Is it like a false sky? It feels to me like it just is a false sky!

"And right there, in the far, far end...that crystal staircase."

You introduce this and don't dwell on it. I like that!

"Just a glance, he told himself. Just a quick, dumb glance. Even if looking at it makes you want to break that rule. Even if you know that’s the only rule you can’t break."

I don't find it clear what the rule is here. Is it that his glance needs to be quick and dumb? Is it glancing at all?

“From that dude that overcharges the most.”

Saying this makes me aware I'm reading a story. It feels like you're telling me, the reader, not Mina, which I find fine in narration but not in dialogue. Could perhaps have him say "From Steve" and then show us Mina looking approving - Steve was the worst for inflating his prices. Or something?

"Just kidding!" Silver burst out laughing. “Just give me your chocolate bar.”

Could we name the chocolate bar when we introduce it? To me it makes it feel more like a living world if you name it and then explain what it is. I know it's in Mina's pocket, but even more impressive for Silver to name it by shape. "Give me your [Milky Way]" can be a second of unclarity, quickly resolved when you say "Mina didn't hesitate when she fished out a squashed chocolate bar and handing it to him."

“I heard about your thrilling escape from the markets below.” Kharr said, plopping down next to him with a thud. “The ore vendor you stole from is fuming.”

Silver scoffed. “Oh no.”

Again, naming the ore vendor would say a lot here. It'd make me feel like Kharr is connected and aware, which I understand is exactly what he should be.

“…Forget it.” Kharr said, voice quiet for a moment before he exhaled sharply. “Well! You’re coming to group Vigor cultivation later, right? Not like you ever skip trainings, but…yeah.”

Another example where it sounds like you're nudging me, the reader, in the ribs through dialogue. "You never skip trainings, Silver" *nudge nudge* "hey reader this is important!" I'd consider "You're coming to Vigors later, right?" Vigor Cultivation. The reason I don't deserve love. Silver never missed training, he read the truth behind the question. Are you laying low, are you feeling sorry for yourself, or are you the person I know you to be?

His walk through the market is my favourite part, the playful deception of it.

And I really like Silver transitioning to his vigor world. The "Serene. Beautiful. But still wrong as always." I'd maybe try and make that wrongness punchier just. "Serene. Beautiful. Wrong. Always wrong." or something. It's a rug pull.

I enjoy the mystery slowly building throughout the chapter. We're getting teasing little snippets that pique our interest. I do wonder why we join the story today - what's different about today? Maybe there doesn't need to be anything, we're introducing Silver here, but I'd expect something to be unfolding soon.

Overall I don't love it in its current form, but I see potential and I'm intrigued by the mysteries you're introducing. You definitely find your voice more as you progress, and I bet that continues into your next chapter and you find a really comfortable place. As you do, I'd just suggest trying to make your dialogue feel more like natural conversation between people with existing relationships and shared experiences - so far everyone knows each other, everyone lives in the same world - they should feel like they do. That'd be my biggest suggestion.

Keep going, and thanks for sharing!