Using AC97 codec with Arduino or STM32
To talk to an AC'97 IC, you'll need a DC'97 ("digital controller " which is just another word for "controller which speaks the AC-link protocol").

Hardware-wise, you'll only find that in older motherboard chipsets - the synchronous 5 wire 12.288MHz link with clock and sync lines is really awkward to work with.

In short: AC'97 is pretty much the last thing you want if you want cheap and easy, unless you are willing to buy a couple tens of thousands of south bridges, and are stuck somewhere between 1998 and 2004.

For a microcontroller- attached audio codec, choose I2S as very simple protocol which is hardware-integrated even in cheap microcontrollers, and can be used for mono or stereo, or even quad channel with an addition of another control line. I2S audio DACs and ADCs are available from many sources and cheap.