Indeed. I also forgot to mention, I did get a Zoom H4n recorder and I had some ungodly set of adapters and it was straightforward to set up for hardware recording of calls and such with high quality. So that's an option that is higher quality but a good bit costlier.

@IvanD your comment prompted me to do a bit of research as I'd love to have a setup that works for this that I can employ when the need arrives. I found a tool called blackhole which is the same functionality as the needed bit from audiohijack or Loopback, both by rogue amoeba and both paid. But blackhole is free and open source! Then I believe we may need to combine it with two things, a multi output device so we can monitor the blackhole output (which is an "input") that we set as the system audio target device, and an aggregate device to combine the input from blackhole and your chosen mic.

no and i have no need for such capability now though may later on. The other day though I was able to watch a movie with another person by creating a combined audio out device with the Audio MIDI Setup utility in macOS. We were both using airpods! That thing seems pretty powerful, so I do feel like it might be possible to set up a virtual device with it that would emit as output both a mic in from some given device and and the regular system output, and then target this virtual device for recording via OBS for example. It may be wishful thinking but there has to be some way to do this.

Ah, crap. So, the Aggregate Device is great with built-in output when no headphones are plugged in. once headphones are plugged in, the computer's speakers are muted, and so is this Aggregate Device.

This software looks to be more powerful than I need. I was able to implement something that seems to work by creating an Aggregate Device (which fuses the corresponding input device and the Built-in Output) using the Audio MIDI Setup app available in OS X/macOS, then using QuickTime Audio recording with that device selected as input. The only thing about this is that if I reduce the system volume to 0 the recording will not catch it. But I believe that this is the correct behavior anyway!

Yes, i see, thank you. I now understand that I can make a suitable circuit for adjusting the line level signal into something suitable for a recording device expecting mic level input by using 3 resistors and one capacitor, which is not ideal but also not impractical to make it portable. Also I have learned that sometimes the mic plug has a DC voltage on it (thats what the cap is for).

@Tetsujin could you help me out and comment a bit more on the differing voltage and impedance on input vs output? Does that mean that my comment is also completely off-base?

Something that strikes me as a possibility without requiring additional hardware is to assemble a “special” TRRS splitter which routes the mic into the Right channel, so that the recorder will receive the Left channel as normal and the Mic on the Right channel, dropping the headphones’ right channel entirely. This is electrically sound and should get the job done as well, but I am thinking that if a product exists that is not bulky that can do proper mixing, I’d prefer that.