There is a software called Solicall which actually allows this. See how no mic's are listed as output devices:

This 'other program' only allows microphone inputs to be used as its input device. The reason I want to do this is to stream audio to the microphone and set the microphone as input device for another program. None of the virtual audio cable related posts on here or internets address this specific limitation. Unfortunately, none of these solutions provide a way to send audio output to a microphone input. More: tried using VAC virtual audio cable, as well as virtual audio streaming.

The VB-Cable virtual audio device is available for free to test and as simple donationware, while VB-Cable A+B package is distributed as donationware – users select a price (€5-25/US$5-25) to get a personal download link after purchase. ‘Many people have asked for a Mac version, but it was not so easy to develop since we wanted to make it a first step for the Voicemeeter porting process.’ While VB-Cable is already widely used on PC as simple virtual audio device, we are proud to finally offer this product for Mac,’ says company founder, Vincent Burel.

VB-Cable for Mac supports up to eight channels in all standard sample rates from 44.1kHz to 192kHz. Users select the input in one application and the output in other, and sound will be transmitted from the source one to the destination. VB-Cable works on installation, without any configuration necessary. It can be used in a recording environment, or to facilitate interconnection between different audio tools. All audio sent to its input is forwarded to its output, making it easy to create audio routes between any audio software by connecting player applications to recorder or capture ones, possibly passing through a DAW to process the sound or VoIP applications.

The VB-Cable is a simple virtual audio device presenting a single input and a single output. VB-Audio virtual cables are now available for macOS (v10.10-10.15/64 bits), supporting connection of audio applications together.

Virtual audio cable for mac