Heat 1 tablespoon of the oil in a cast iron skillet over high heat. Toss the spare ribs in the flour just to coat. Working in batches, add the spare ribs to the pan and cook until browned on all sides, 10–15 minutes.

Using sauté mode on an Instant Pot, heat the remaining 1 tablespoon oil. Add the onion and sauté until translucent, about 5 minutes. Add the spare ribs.

In a bowl, combine the brown sugar, vinegar, pineapple juice, shoyu, water, garlic, and ginger and mix well. Pour the mixture into the pot. Press 'cancel.' Lock the lid in place and set to sealing. Cook on high pressure for 25 minutes. Release the pressure naturally for 10 minutes, then manually release the remaining pressure, press 'cancel,' and remove the lid.

To make the sweet potatoes: Bring a few inches of water to a boil in a pot fitted with a steamer basket. Add the sweet potatoes. Cover, reduce the heat to medium, and steam until the potatoes are fork-tender, 25–30 minutes.

Slice the potatoes on the bias about 1 inch thick and place on a cutting board or baking sheet. Using a heavy-bottomed cup or bowl, flatten the potatoes. Season with the garlic salt and pepper.

Heat the oil in a large skillet over medium-high heat. Add the potatoes and fry until crispy, 10–15 minutes. Flip and repeat on the other side.

In a small bowl, whisk together the cornstarch and water. Add the mixture to the Instant Pot and stir to thicken the sauce. Stir in the pineapple chunks and serve with the smashed purple sweet potatoes.