nouns - Can a preposition be before an adverb?

Ok, this site says

The preposition is almost always before the noun or pronoun and that
is why it is called a preposition

Now, this oxford dictionary says

here (adverb)

used after a verb or preposition to mean ‘in, at or to this
position or place’

I live here.

Put the box here.

Let's get out of here.

Come over here.

So, the dictionary says "here is an adverb & we can put a preposition before here"

Eg: I am in here

I would say the dictionary is not correct, "here" in "in here" is a pronoun or noun. But I am not sure.

The same thing happened to "there".

Eg: he is in there; he is up there

Can a preposition be before an adverb?