How do I convert a left or right channel to mono?

I have a wav file with three channels. When I open it in Audacity 2.2.1 (on Ubuntu 18.04.1), I see the track information in the attached screenshot. The tracks are listed as single channel tracks “Left”, “Right”, and “Mono”. If I try to mix and render eg. the “Left” and “Right” channels I just get a stereo track. No mixing is done.

How do I make Audacity treat these tracks simply as mono channels? Opening the track menu doesn’t provide any options for this. Using “Tracks > Pan” doesn’t help, since you can’t really pan a single channel (I tried it anyway though). Looking at the track information area section of the manual, I only see “Stereo” and “Mono” as possibilities, so no help there.

How do I just work on three mono channels?

Click on the name of the track, then select “Mono” from the menu that appears.

Sorry, I don’t see it. Is this (attached) the menu you mean?

(I also forgot to mention the third required piece of information: I’m using Audacity from Ubuntu’s repositories.)

Are you working on an Audacity project that was created with an earlier version of Audacity?

Scratch that. It appears to be a bug in Audacity 2.2.1 that I wasn’t aware of (it is fixed in the current 2.3.1 version, but that version is not yet in the repositories).

There’s a simple workaround:

When you import a 3 channel track, it imports as three tracks, as shown in your first post. The track order is: Left, Right, Mono.
Click on the name of the first (“Left”) track, and from the dropdown menu, select “Make Stereo track”.
The “Left” and “Right” tracks will be combined into a stereo track.
Then click on the name of the stereo track, and select “Split to Mono”.