Combine the light brown sugar and water in a medium saucepan and heat gently over low to medium-low heat, stirring until the sugar fully dissolves. Add the cinnamon stick, apple cubes, and cranberries, bring just to a light simmer, then reduce the heat and let the mixture infuse for 8–10 minutes, until the cranberries burst and the apples release aroma; do not boil aggressively, as this is extraction, not reduction.
Remove the saucepan from heat and strain the mixture through a fine-mesh sieve into a bowl or measuring jug, pressing very gently to extract liquid without forcing pulp through. Discard the solids and the cinnamon stick, then let the syrup cool completely.
Pour the cooled apple cranberry syrup into a large pitcher, add the ice-cold water, and stir gently until fully combined and clean.
Refrigerate for 1–2 hours until fully cold and the flavors are integrated.
Fill glasses with ice, pour over the apple cranberry drink, and garnish with apple slices and fresh cranberries.
