Last iPad with RCA/phono input

For iPad models that do not feature a built-in 3.5mm audio jack, you can add a wired 3.5mm audio connection by using an appropriate adapter:

• USB-C to 3.5mm Headphone Jack Adapter

https://store.apple.com/xc/product/MW2Q3ZM/A

• Lightning to 3.5mm Headphone Jack Adapter

https://store.apple.com/xc/product/MMX62ZM/A

iPad9 was the last one with a 3.5mm minijack which would feature stereo out and mono mic input

iPads have never had RCA or phono inputs.

For other audio connections, USB-C audio input works, too: https://www.audio-technica.com/en-us/support/audio-solutions-question-of-the-week-is-the-atr2500x-usb-microphone-compatible-with-my-ipad-pro