What does "It is not everyone who has your passion for dead leaves " mean?

I am currently reading Sense and Sensibility and came across the following passage.

"It is not every one," said Elinor, "who has your passion for dead leaves.

Since I’m not a native speaker , I have some difficulty analyzing the sentence:

It is not everyone who has your passion for dead leaves

What does it mean? I would like to understand the structure of the sentence rather than the meaning. I know that this sentence means that not everybody has passion for dead leaves. But what does the part of the sentence, It is not everyone, mean? Also other similar examples would be great.

It is not everyone who has your passion for dead leaves.

We can guess that the context has someone who likes to look at or keep dead leaves (maybe for the fine artful network of veins left behind after the rest decays away), who also tries to get someone else interested in dead leaves, prompting this sentence in response. It parses as follows:

It is { not everyone } { who has ... }.

It is X [subordinate clause].

This is sometimes identified as a type of cleft sentence, where "It is" is a fixed construction that does not change even if X is plural:

It is they who are lying.

Other examples with different X and different kinds of subordinate clauses are:

It is { she } { to whom we owe our thanks }.

It is { he } { whose bag has gone missing }.

It is { for this } { that I have come }.

It was { those books } { that you gave to me }.

And here are some examples in question form:

Is it { she } { to whom the books belong }?

Who is { it } { whose bag has gone missing }?

Is it { for nothing } { that I have come }?

Which books was { it } { that you gave to me }?

A more complicated example:

It is { not everyone who speaks } { who understands what they are talking about }.

Anyway it is indeed not easy to analyze this kind of construction, and even native speakers might not be able to give an explanation. Grammarians still disagree on what exactly the subordinate clause is. All that you need to know is how to use them, which is that the subordinate clause follows the same rules as relative clauses.