In Merriam-Webster, our dictionary of choice, the hyphenated compound noun “decision-making” appears as such, so it's always hyphenated. (Most adjective forms, on the other hand, can be left open after a noun, even if they are listed in the dictionary with a hyphen.)

Does decision-maker have a hyphen?

Use a hyphen if the term is used as an adjective: XYZ is a decision-maker tool. Do not use a hyphen if the term is used as a noun phrase: She is a decision maker.

Is decision-making hyphenated AP style?

decision-maker, decision-making: Hyphenated in AP usage. default: Failure to meet financial obligations.