A recent report by WABetaInfo suggests that the feature is currently available on the official beta channel and will be rolling out to users in the coming days.

Source: https://indianexpress.com/article/technology/tech-news-technology/whatsapp-for-windows-gets-call-link-feature-that-lets-users-quickly-add-others-on-a-call-8474554/

It is worth mentioning that there was a leak of the WhatsApp group voice chats feature earlier, when it was being tested through WABetaInfo, when it was still in its testing phase and it was still being tested.

Source: https://www.chiangraitimes.com/tech/whatsapp-you-can-chat-with-many-people/