Does Vor allem phrase change as per cases?

Question

I am assuming that vor allem is a fixed phrase. Vor allem has different meanings in the Pons dictionary. Whenever the word "especially" is translated to the German "vor allem", it does not matter what noun and case is next. Evrytime, it takes allem .

Why cannot we use vor alle/allen in nominative position or accusative position. Is it mandatory to write vor allem always?

I have checked similar questions, already asked in the forum but, that did not clear my doubt.

Example: (Taken from Pons dictionary)

Vor allem Frauen sollen dafür qualifiziert werden.

This is my translated example (I had written vor alle but the translator shows vor allem Jugendliche):

Vor allem Jugendliche sind immer auf der Suche ....

Answer 1

The fixed phrase "vor allem" is an adverb and can be replaced by e.g. "besonders", "insbesondere", "in erster Linie" or "vor allen Dingen".

See e.g. https://www.wortbedeutung.info/vor_allem/ or https://de.wiktionary.org/wiki/vor_allem

For this meaning you have to use the fixed phrase unchanged, independent from the case or number of the noun following it.

The example sentence

Vor allem Frauen sollen dafür qualifiziert werden.

could be translated to English as

Especially women should get qualified for this.

emphasizing that it is particularly important for women.

The adverb "vor allem" can not only emphasize a noun but also other words like a verb, adverb, adjective.

Modified examples:

Frauen sollen vor allem dafür qualifiziert werden. (emphasizing "dafür")

Frauen sollen dafür vor allem qualifiziert werden. (emphasizing "qualifiziert")

The other example

Vor allem Jugendliche sind immer auf der Suche ...

is correct. Your wrong translation "vor alle Jugendliche" would not make sense in this sentence without other changes because this would turn the subject "Jugendliche" into a part of an adverbial "vor alle Jugendliche".

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If instead of "allem" you use a form that matches the noun like

Vor allen Frauen ... (Dativ, location, static))

or

Vor alle Frauen ... (Akkusativ, direction, change)

it is no longer a fixed phrase but a combination of a two-case preposition (Wechselpräposition) "vor" and an indefinite pronoun (Indefinitpronomen) "alle". Depending on the context, this would change the meaning to

In front of all women / before all women ...

This would not make sense in the example sentence without other modifications as already explained above for your other example sentence.