In RB there is yet another way.
Merge the track to compressed file.
Solo the track then use the above command so you only get that track in the end result.

When asked for a file type - pick PCM MONO, and you get a 16/44 MONO track as the end result.

.. not sure if BiaB has this also.

And yet another way to try (a little more complicated but should give you a MONO track in RB ..).

Set a Blank track as MONO. (important)
Select the desired source track (or tracks)

Then, in Charlie's image, up about a dozen options is a 'Merge' selection.
This looks like it will be something you already know about, but clicking this reveals a way to merge tracks in your RB project to a single RB track.
If the target track is MONO, going from memory, RB asks if you want to make it a stereo track .. say no and you end up with a new MONO audio track without ever leaving RB.

Attached Files (Click to download or enlarge) (Only available when you are logged in)
RB_mergeSimple.jpg (74.41 KB, 17 downloads)
Last edited by rharv; 04/08/20 11:34 AM.

Make your sound your own!
.. I do not work here, but the benefits are still awesome