Does my Talabat total count in the day's sales, and how does the POS know it?

You type it. Name your delivery apps under Settings → The POS, Totals typed at closing, up to twelve, and the closing screen asks for each app's own total for the day. That figure is added to the day's total in the day report and the WhatsApp summary, and the orders the app sent through Get Menu come off so nothing is counted twice. The same section takes your card machines, checked against the card payments the POS took, and expenses paid by card. None of it touches the drawer, because the app holds the money. The Orders from delivery apps tab in the docs covers the money side.