In a large mixing bowl, combine the strawberries, blueberries, peach slices, and grapes.
In a small bowl, whisk together the white balsamic vinegar, honey or maple syrup (if using), lemon juice, basil olive oil, and a pinch of salt until well combined.
Pour the dressing over the fruit and gently toss to coat all the pieces evenly.
Transfer the fruit salad to a serving bowl. Garnish with fresh mint leaves.
Serve immediately, or refrigerate for up to 2 hours to allow the flavors to blend.