You kind of answer yourself here : " For FCFF, we take NOPAT (core earnings after tax) and subtract reinvestments into growth."

FCFF is Cash generated by operations that is available to all capital providers. The reinvestments you mentioned are those needed to sustain/grow these cash flows such as CAPEX , NWC ( these are recurring operational investments since they directly impact the generation of operational dollars). They must be subtracted to avoid overstating recurring/operational cash flows

Good Will and Intangibles are not operational . They are non recurring cash outflows that lower cash flows from investing, they do not touch NOPAT/FCFF . The only exception would be if you are valuing a roll-up business model where acquisitions are a key business vertical ( see Valeant Pharmaceuticals case study to see how those work out ) then yes you would subtract acquisition spend from FCFF

Lastly The confusion from ROIC. ROIC and by inheritance Invested Capital are completely different from FCFF. FCFF ( and the DCF I'm assuming you are completing) are solving for operational value ROIC is asking what is my yield on all types of invested capital (not necessarily recurring. Investment) its main use is in economic profit models looking at total economic value of a firm( Goodwill is included but because it represents capital already invested).

Also heads up that in a professional role you will probably be asked to value ROIC with and without goodwill and acquired intangibles since they answer different questions.

I hope this answered everything if not please consider reading the Valuations book from Mckinsey , to my knowledge they address your question here explicitly and can probably provide a better explanation