Preheat the pressure cooker (by pressing brown/sauté mode).
Add the sesame oil and brown the cabbage wedges on one side (about 3 minutes). In the meantime, grate the carrot. To the pressure cooker add the 1 1/4 cups water, vinegar, sugar, cayenne, and red pepper flakes and swish around. Then add the cabbage wedges (browned side facing up) and sprinkle carrots on top.
Close the lid and pressure cook for 5 minutes at high pressure. When time is up, open the pressure cooker with Normal Pressure Release (twist the valve on the lid to the “open” or “venting” position). Remove the lid tilting it away from you.
Arrange the wedges and any loose leaves onto a serving platter. Reheat the cooking liquid (by pressing brown/sauté mode) to a boil. In a small bowl, mix the cornstarch and 2 teaspoons of water to make a slurry. Then pour the slurry into the pressure-cooker base.
Boil the cooking liquid mixture until it's just starting to thicken. Pour this sauce over the cabbage wedges and serve.