Add half the water, tea bags, and blackberries to Instant Pot and stir to combine. Lock the lid and set the vent to sealing. Select the pressure cook button and set the time to 5 minutes.
When cook time is complete, allow pressure to release naturally for 5 minutes, then do a quick release. Remove the lid and discard the tea bags..
Add the basil, honey, and lemon juice and let stand for 10 minutes.
Strain the tea over a fine mesh strainer into a heat-resistant pitcher. Add remaining 4 cups of cold water. Cool completely.
Serve over ice with fresh blackberries and a sprig of fresh basil for garnish.
Notes
Fresh blackberries will give your iced tea a vibrant, fresh flavor, but frozen blackberries can be a great alternative, especially when fresh ones aren't in season.
Black tea is a classic choice for its robust flavor that pairs well with the sweetness of blackberries.
For the best results, use high-quality tea bags or loose-leaf tea to ensure your iced tea has a rich, full-bodied taste that complements the fruitiness of the blackberries.