External Mic Recognizes As Output on iMac

Based on the OP's tag line, he has a 24" M1 iMac. No other 24" iMac is recent enough to run macOS 13.5 Ventura.

These articles – especially the second - suggest that the 3.5mm headphone jack on a 24" M1 iMac might accept mono microphone input.

About the audio ports on Mac - Apple Support

Change the sound input settings on Mac - Apple Support

A little more digging turned up this. Although this is about a M1 Mac Mini, it sounds like it might apply to the 24" M1 iMac, as well. That is, the input jack likely accepts a three-ring plug (for a stereo headset with a mono microphone), but not a two-ring plug (for a stereo microphone).

https://apple.stackexchange.com/questions/438545/audio-input-on-mac-mini-m1-2020

dollykenk wrote:

Rode VideoMic GO displays as output source on iMac. I am trying to record a voiceover using my mic within iMovie however, iMovie cannot recognize the rode mic and is not available. Whether I plug the microphone in directly to the desktop computer headphone port or utilize my Hyper Drive Dock, there's no luck. I would like to know how to switch from the Rode VideoMic Go showing as an output source "headphone" to display as a an input source "external microphone". How do I fix this?

One option might be to get a USB sound card (with audio input). Plug the microphone into the USB sound card, and the USB sound card into your computer or dock.

There's also this:

https://www.amazon.com/Rode-SC4-Microphone-Cable-Inches/dp/B00L6C8PN0/

But if you have a stereo microphone, you might want to put the $15 towards a USB sound card, rather than towards a cable that combined the left and right channels into a mono signal.

Is it plugged into the audio out port? The headphone port?