The Blackbird component doesn’t make a lot of sense as you present it here, unfortunately. Agatha’s tired of living a simple and quiet life… but she’s got a mysterious secret persona which is presumably the opposite of this? Unless the violent brush with danger is related to why she stopped being Blackbird previously?

If so, I’d bring that information up front if you can. Something like “Agatha had a secret persona, Blackbird, which she used for [activities/reasons]. After [incident in her youth], she decided to attempt living a quiet life as a magictecture parchment maker, but she misses a life of challenge and adventure.

When prim and proper detective Graham seeks her help to locate the mysterious Blackbird for [reasons], Agatha agrees to help him because [presumably to throw him off the scent? But if not you should explain why she wants to help someone who could discover her secret]. But when [stakes escalate] she must once again resume her Blackbird mantle.”

as happens often enough, it starts well, then falls apart.

first, for adult, you rarely need the age unless it informs the pitch, which i don't think is happening here. so you can begin with agatha. i think magitecture parchment is a cool idea, but quiet life is vague and easy enough to show. then, i'm not quite clear on her hands because i don't know what the prosthetics are. so are you saying she e.g. can't use her hands to drive but can use them to do magitecture whatevering? and then the adventure language gives you a spot for specificity, and the violent brush is vague.

the next paragraph introduces a revolution we didn't see before and which we probably should have. i'm not sure you need it, though -- you can have other magitects doing things and agatha being trapped anyway. but are the prosthese the reason? it's unclear, and building a sympathetic character means being clear about the reason.

then graham is sudden, which might be organic to the plot, but what probably isn't is blackbird being sudden. we don't know there are legendary anythings. one place to put that is the challenge/adventure language in the first paragraph. then the criminal syndicate is sudden and we could have known about its involvement in the mortan danger language.

the high academy is sudden and i'm not sure we need it, nor am i sure we need much of the language in that paragraph. and then the last one is full of vague and sudden and i'd have liked a touch more foreshadowing that she's blackbird.

does this query cover more than half the book? the twist -- that she's blackbird -- feels a bit end-of-bookish to me. the query should cover only 30 to 50 percent.

in any event, you do a solid job keeping to character and motivation, so your needs here are clarity and process.

good luck <3

It will appeal to readers who felt for the plight of extraordinarily talented woman facing misogynistic systems of power in Blood Over Bright Haven by M.L. Wang and class struggles on a backdrop of rapidly developing magical science in the show Arcane.

Less and less do I like stuff like the bolded bits. These are the kinds of things that should be clear from your query and can go unspoken. Think I had more success when I stopped trying these little tricks upfront. Going through the rest of your query, I don't really see misogynistic systems of power, or a class struggle. My feeling is if you feel the need to say sell it upfront like that, it's because the body of your query isn't really done.

At 32 Agatha is the best magitecture parchment maker in the city...

Don't read a ton of fantasy, but are we supposed to know what this means?

...and tired of convincing herself that she is satisfied with a quiet life.

This is a more interesting thought than the first half of the sentence.

Her hands only work encased in delicate clockwork prosthetics but her mind longs for a challenge and adventure — something she did not allow herself to think about since the violent brush with mortal danger in her youth.

I don't understand how the part about her hands flows into the part about her mind. Last part of the sentence is vague. Why not tell us what exactly this violent brush with mortal danger in her youth was? Without knowing what it is, we don't fully understand why she doesn't allow herself to dream of adventure.

Now, the magitecture revolution is happening, each day bringing in a new glorious invention, but Agatha’s role in it is pushed to the utilitarian basics: supplying sharpest minds with materials to build the bright future on.

I don't understand what any of this means, not a word of it. What is the magitecture revolution? Who are they revolting against? What even is magitecture? Why does a revolution bring a new invention? Why is Agatha, the best magitecture in the city, acting in a reduced capacity? Who are the "sharpest minds?" Isn't Agatha one of the sharpest minds? What bright future is being built?

And more importantly, I don't understand why it's happening or how it's affecting Agatha.

So when prime and proper detective Graham comes to ask for her expertise in his search for a mysterious legendary magitector Blackbird, Agatha agrees to aid him. That quickly gets her tangled in his one-man-war with a criminal syndicate. Same one she barely survived many years ago.

Why does Graham choose Agatha? What does this criminal syndicate want?

As Agatha researches the ways magitecture is used by the criminals, she discovers their ties with the High Academy, making her an enemy of both the underworld and the highest seat of power at the same time.

There's so many groups and factions here that show up really close to each other. A criminal syndicate, a high academy, an underworld, a high seat of power, and in the next paragraph, we add corrupt policemen.

Agatha has no other choice but resume her Blackbird mantle once again

Of course she has a choice. Always dislike when queries say the MC has no choice. The whole driving force of narrative is choice.

or this time be silenced for good and let her legacy be stained forever by people who stole her groundbreaking work.

Don't understand what her legacy is or what her groundbreaking work is.

Definitely quite a few "first attempt" issues here, which are:

1) You're juggling blurb language and query language.

2) You're too close to your work right now to fully understand how to translate it to someone who doesn't know anything about it.

3) You're trying too hard to communicate a bunch of stuff you find interesting about your world, instead of focusing on communicating who your main character is, what she wants, what's standing in her way, what happens if she fails, and the promise of a thrilling conclusion.