Combine the blackberries, allulose, and lemon juice in a small saucepan. Cook over medium heat for 6 to 8 minutes, stirring and crushing the berries until thick and glossy.
Press the blackberry mixture through a fine-mesh strainer and discard the seeds. Refrigerate the smooth ripple until completely cold.
Blend the heavy cream, almond milk, powdered allulose, goat cheese, vanilla extract, xanthan gum, and sea salt until silky and uniform.
Refrigerate the goat cheese mixture for at least 3 hours or until thoroughly chilled.
Churn the mixture in an ice cream maker according to the manufacturer's directions until thick and creamy.
Spoon the ice cream into a freezer-safe container, layering it with the blackberry ripple. Freeze for 3 to 4 hours before scooping.