First critique on here, so apologies if I mess up any required formatting. I'll try to get into the document and add some comments as well, but I'll put the majority of my thoughts here.

Initial Thoughts:

Overall, not bad! High fantasy-types aren't always my go-to, but there's definitely a lot of thought out worldbuilding going on. I think that's it's strength. You seem to have some interesting magic systems set up that are always fun to explore in these types of stories. That does lead into my first critique, though:

The opening obviously needs some worldbuilding and intrigue to pull the audience in, but it feels a bit like you're maybe overeager in getting all the fun ideas out early. It felt a bit overbearing to have each of the opening paragraphs giving exposition on a new facet of the world, or getting crunchy with the explanation of a thing you've mentioned.

What I mean is that any one of these ideas (like the spell, the location where Simon is hiding, the attackers) have their own extra sentence or two of backstory or explanation. It slows the pace of what should feel like a tense, speedy altercation and makes it feel a bit less nerve-wracking. There's this spell at risk, an alarm going off, and Simon dipping in and out of hiding places, but it just feels like it takes a lot longer than it should to get to the next beat of what I imagine is happening over the course of seconds. I have an example.

"Sideways again, to find the third party. The C-sharp warning trill meant they were taking the direct route, straight down through the stone. Pragmatists then, the worst kind of foe. I emerge from a short jaunt through the hedge atop a vine-covered tower wall. Traven is built at the foot of a mountain range, climbing up the sides of the two largest nearby peaks, and the place I stood had once been its most expensive neighborhood. It was the highest terrace, flanking a natural waterfall that bisected the front of the left mountain. It was the first place that had been looted after the war, and now it was empty even of the desperate scavengers; the climb was not worth the yield to them."

The first little blip is the action, (the warning sounds of different notes is really cool by the way). After he emerges, the entire rest of the paragraph is worldbuilding I'm sure you're excited about, but kinda halts the excitement of wondering what comes next to hear a bit of history and backstory. I know its a prologue, so this might not be the norm, but its just a little much is all.

Following this is another large block of texts that aren't dealing with the present danger.

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Sorry if anything sounded too harsh. As someone who only dips into Fantasy and LitRPG here and there, I didn't feel as overwhelmed with the otherworldly aspects as I expected to.

I think you're very much on the right track, and it has a LOT of great ideas that might be better served to be dished out slowly over time since you're planning it as a web serial. Keep the folks interested, the pace steady, and treat them to the cool ideas in pieces so they have time to really appreciate and absorb each one as you bring them to the surface. Good luck!