You appear to have linked the canonical, which has a few duplicates marked. All are asking about isolating one channel, as far as I can tell. This canonical is literally titled "ffmpeg: isolate one audio channel". One of them also asks about "downmixing" to mono after isolating the channel (which I guess means marking the audio format as mono so that that isolated channel will play on both speakers), but that is trivial. And you see the same basic techniques offered in the answers: to use `-map-channel` or the `pan` audio filter. The other one explicitly wants a panned result, i.e. still stereo but only on one side; the logic for this is clear from the explanation in the canonical answer.

The point is to show the technique, not to meet individual exact needs. Stack Overflow doesn't need separate "how do I get the second line of a file?" and "how do I get the third line of a file?" questions.