The Voice Focus feature is only available on selected A-series models for the Indian market and not elsewhere. Your particular model already has noise cancellation built-in via a secondary microphone.
Any info you have gleaned, either via Google or YouTube is India based (ever seen a video which isn't from India?). Forget what you read on Samsung forums etc as they simply aren't or won't be aware this is a feature only available for that market.
When the microphone is first activated, whether at the start of a call, using Google Assistant, Shazam or whatever, you will briefly see the green microphone icon shown on the top right of the display before turning to a green dot showing that the microphone is active.
Your phone already has noise cancellation built-in so forget about VF and just enjoy your new phone.