Leave the nectarines unpeeled and use a serrated knife to slice them into 3/4-inch-thick wedges. You will end up with about 6 cups of sliced nectarines.
Coat the inner pot of the Instant Pot with cooking spray or lightly grease with oil.
Add the sliced nectarines and blueberries to the inner pot. Top with the cane sugar, brown sugar, a pinch of salt, cinnamon, ginger, cardamom (if using), almond extract (or vanilla extract), and lemon juice. Stir gently to coat the fruit.
Secure the lid and set the Pressure Release to Sealing. Select the Pressure Cook setting at high pressure and set the cook time to 1 minute.
Meanwhile, prepare the Crisp Topping: In a large skillet, heat the coconut oil over medium heat. Once the oil is melted and hot, add the oats, almond flour, pecans, brown sugar, cinnamon, and salt. Cook, tossing frequently to prevent burning, until toasted and lightly browned, 5 to 7 minutes. Carefully transfer the crisp topping to a large piece of parchment paper and spread out to cool slightly.
Once the 1-minute timer has completed and beeps, perform a quick pressure release by carefully switching the Pressure Release knob from Sealing to Venting.
In a small bowl, whisk together the cornstarch with 1 tablespoon water until dissolved into a slurry. Open the pot and pour the slurry into the nectarine-blueberry filling. Select the Sauté setting and bring to a boil, stirring gently until the filling has thickened, 1 to 2 minutes.
Transfer the nectarine-blueberry filling to a large serving bowl or individual dessert bowls and sprinkle generously with the Crisp Topping. Serve warm with vegan vanilla ice cream if desired.