which external microphone is compatible for mac mini to convery speech to text

Any mic connected to the headphone port will do. Use a combo headset with built-in mic like this one https://www.apple.com/shop/product/MNHF2AM/A/earpods-with-35-mm-headphone-plug or a TRRS splitter shown below for use with an external mic. Note the 3 rings on the connector, one with 2 rings won’t do.

They should all work - maybe someone else will chip in with a recommendation.

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