Combine granulated sugar and water in a small saucepan over medium heat, stirring until sugar is completely dissolved to create a simple syrup.

Remove simple syrup from heat and allow to cool to room temperature.

In a high-speed blender, combine the blueberries, sliced peaches, cooled simple syrup, lemon juice, and salt.

Process the mixture on high speed until completely smooth.

Pass the puree through a fine-mesh sieve into a clean bowl to remove fruit skins and seeds for a smoother texture.

Cover and refrigerate the mixture for at least 2 hours until thoroughly chilled.

Pour the chilled puree into an ice cream maker and churn according to the manufacturer's instructions until it reaches a soft-serve consistency.

Transfer the churned sorbet to a freezer-safe container and freeze for an additional 4 hours or until firm.