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 ...
It should be either "Neue Karte" or "Neu" but not "Neue".
It's different in other languages by the way. Say, in Russian, you would specify the gender even if the noun is missing. But in German, if the label of a button in some software is shortened to just one word, the adverb is used, which carries no gender ending.