Place the chicken, celery, potato, onion, vegetable broth, baby carrots, brown rice, parsley, minced garlic, thyme, sea salt, black pepper, and cayenne pepper inside of an electric pressure cooker and stir to combine.
Place the lid on the cooker and make sure the vent valve is in the SEALING position. Using the display panel, select the MANUAL/PRESSURE COOK function, high pressure, and use the +/- buttons until the display says 12 minutes.
When the cooker beeps to let you know it’s finished, switch the vent valve from the SEALING to the VENTING position. Use caution while the steam escapes—it’s hot. Remove the lid and stir in the yellow squash. Place the lid back on the pot and let the squash cook for 2 to 5 minutes, or until tender. Serve warm with fresh herbs and a squeeze of lemon, if desired.