I know that wav and flac (I prefere looseless) can store more than 2 channels. I try to export and no. There is only stereo or mono option.
It would be nice if I can export music in 2 channels stereo (to play left and right ears separately), And voice to mono (to play both ears same sound) but at channel 3.
But Audacity merges all tracks just to stereo 2 channels max atm.
How would you play that file? Most audio players expect audio to be one or two channels only.
You can export multi-channel audio files by enabling “Advanced Mixing Options” in Preferences. See: https://manual.audacityteam.org/man/import_export_preferences.html
Thanks for reply!
I have tried this setting now. And this is not exact what I expected.
The first thing is that resulting file have lost information about what output channel should play in what ear (Left or Right).
So seems that player will play them as all mono. Also when I opened the resulting file in Audacity I got this:
And before export it was another:
*btw: I know that I can “Make stereo track” from 2 tracks. But that is not the point.
Second thing is that when I try to export again I have to configure bindings of multi channels again (coz it was not remembered).
It would be good if we have ability to mark each output channel as one of a ear_kind ~ { Left, Right, Mono }.
Also maybe have separate flag “extra” or ‘hidden’ on them.
I do not know much about audio file format specification (if those marks and flags are supported). If we currently do not have such file formats then I wish it to appear in near future 
Back to “*btw:” ~ When I open multi channel audio in Audacity I want it to do “Make stereo track” automatically in cases when Left_channel and Right_channel are present in a sequence close together. Or maybe have an option to do it in settings (So be able to turn this off).
Audio files don’t carry that information. The audio files just have channels 1, 2, 3,… It’s up to the player to decide which channel to play through which speaker. In the usual case this is simple - all players play 2 channel audio with channel 1 to the left speaker and channel 2 to the right.
It gets more complicated with multi-channel audio (more than 2 channels), and partly depends on the file format. Some standard channel allocations are shown here: https://en.wikipedia.org/wiki/Surround_sound#Channel_identification