Duplicating one (mono) track to another

My apologies if this has been covered before; I have tried searching but the answers seem to relate to have a single mono timeline and making it stereo.
I have a stereo audio file but only the left channel has been recorded, so effetively a mono track from the left speaker… I want to duplicate the single left channel onto the right to give a left-and-right populated timeline.
Can someone please point me in the right direction to do this?
Thank you.

Firstly, you don’t need to duplicate the track. A “true” mono track will play through both speakers.

What you need to do is to split the stereo track into two mono tracks (“Split to mono”). See: https://manual.audacityteam.org/man/splitting_and_joining_stereo_tracks.html

Then delete the empty track by clicking the [X] in the top left corner of the track.

OK, thank you for that, I understand the process, but that gives me a mono track which only plays through the left speaker.
Going back to my original query, how can I duplicate the left channel to the right so that it plays through both left and right speakers?

OK, got it, I selected all, Mix and Render to new track (which gave me another left-only timeline) then selected all again in the original and pasted into the new track. Lond winded but I got what I needed. Thanks for the advice, Steve.

Ensure that you use the option “Split Stereo to Mono” and NOT “Split Stereo Track”.