The Call tab is the short one — it covers how you're told about an incoming WhatsApp call, separately from chat.
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How a call reaches you
Allow sound notifications for incoming calls is the ringtone: leave it on and a call rings while you have the inbox open, rather than relying on a silent pop-up. Beside it, Available to take calls marks your status for calls. Worth knowing either way: when a call comes in and the inbox is open in a background tab, your operating system raises its own call alert too, so you're told even when the app isn't the window you're looking at — which is why a call is harder to miss than a chat. As with chat sound, the ringtone only plays through a tab that's actually open.