In a large bowl, combine the strawberries, lychees, and granulated sugar. Set aside to macerate while preparing the biscuits.
Heat the oven to 400°F. In a large bowl, whisk together flour, granulated sugar, baking powder, baking soda, and salt. Add the butter and combine into the dry ingredients by rubbing with your fingertips until they form coarse crumbs.
Drizzle in the kefir and gently fold together using a silicone spatula until a shaggy dough forms. Pour the dough onto a floured work surface and use your hands or a rolling pin to flatten it into a 1-inch thick rectangle. Cut the dough into 4 pieces and stack them on one another. Press down again to flatten into a 1-inch thick rectangle. Use a sharp knife or bench scraper to cut into 8 equal pieces. Transfer to a parchment paper-lined baking sheet, placing the biscuits at least 1 inch apart.
Brush the tops of the dough with additional kefir and sprinkle with a thin layer of additional granulated sugar. Bake at 400F for 20-25 minutes until golden brown.
In a large bowl, whisk together the heavy cream and granulated sugar until soft peaks form.
To assemble the strawberry lychee shortcakes, cut the biscuits in half crosswise. Top biscuits with strawberry lychee mixture (make sure to drizzle on some of the strawberry lychee juice) and a generous dollop of whipped cream. Serve immediately.
