In my experience, with the 92HD95:
- The jack supports TRRS connections of the common left-right-ground-mic standard. This can thus have a stereo output and mono microphone input simultaneously.
- When a jack is plugged in, it is possible to switch between headphone and internal speaker output.
- When a jack with a microphone is plugged in, it does not appear possible to switch between the external and internal microphone. Trying to change the settings just gives the same external microphone signal.
- The microphone cutoff switch affects the internal microphone only.
- Looking at the codec chip documentation and messing with alsa and pipewire, it would appear that, unless Framework has done something different, the jack would not support stereo line in (eg, using the TR-- for input), and would not support stereo microphone input in any other way. All of these would be uncommon: the only case I can remember supporting things like these was, if I recall, on a Macbook Pro, and that jack was also a combination with an optical in/out, if I recall correctly.
- The internal mics do appear to have a real stereo input, but there appears to be no way to have external stereo input.
Realistically, for other use cases, it probably makes more sense to use a specific USB-C audio interface.