Voice Reduction Problem

I am using an iMac (Intel) running OS 10.13.6 (High Sierra) and have downloaded the latest version of Audacity. I am using the latest Mac version of Audacity ( 2.4.2) which I just downloaded. I am trying to reduce vocals on a stereo Mp3 Track and am using the INVERT method which seems to be the most popular method I can find. So, following instructions carefully, Step 1- I import the track, Step 2- using the pull down window on the left side, split stereo tracks which works fine. Step 3- using the EFFECT tab on the top, choose INVERT. Step 4- I go back to pull down window on the left and choose MONO on both tracks but herein lies the problem, on the version I am using, there is NO MONO function. I would appreciate any guidance you can give me as to what might be the problem. Many thanks.

Move the pan sliders on both (split) tracks to the centre, that’s the same as MONO.

Thanks, will give it a try!