Learn Polish: W firmie nie mówi się o szefach niechętnych zmianom. - In the company, one does not talk about bosses averse to changes.

The adjective niechętny (averse/reluctant) belongs to a group of adjectives that require the Dative case for the object they are directed at. Since the bosses are averse to "changes" (zmiany), that word takes the Dative plural form zmianom.

What case is niechętnych in, and what dictates that?

It is in the Locative plural to agree with the noun it modifies, szefach. The preposition o (about) forces the noun into the Locative case, and the adjective must match its noun's case, even though it governs a completely different case (zmianom) for its own object.

Why is the adjective phrase niechętnych zmianom placed after the noun szefach?

While single adjectives usually precede nouns in Polish, adjectives that are expanded with their own complements (like niechętnych zmianom) are typically placed after the noun. This behaves similarly to English, where we say "bosses averse to changes" rather than "averse to changes bosses."

Why use the impersonal nie mówi się instead of the third-person plural nie mówią?

The impersonal się construction (nie mówi się) translates closely to "one does not talk" or "it is not spoken of." At the B2 level, this is the preferred and most natural way to describe general facts, unspoken rules, or company culture, whereas nie mówią would sound like a specific "they" are not talking.