I enabled R6 multi-controller through the customized buttons, but I don't see anything happening in the viewfinder or LCD when I press it. Wondering if I am missing something? Any guidance on its operation. Thanks.
You enabled it for Direct AF point selection, correct?
For that to work, an AF mode which allows manual AF point selection must be active.
But in Face+Tracking, the multi-controller should allow you to jump between detected eyes/faces.
Also, be sure that the Multi-Function Lock button wasn't pressed, as it applies to the Multi-Controller as well.