Combine chicken stock, rice, mushrooms, garlic, carrots, celery, sweet potato, onion, bay leaf, and Old Bay Seasoning in Instant Pot pressure cooker. Stir to combine. Cover and set vent to “sealing”. Cook on manual (high pressure) for 25 minutes. Let the Instant Pot rest for an extra 10 minutes (natural release). Then carefully turn the vent to “venting” and release the remaining pressure (quick release). Remove lid and discard bay leaf. During last 10 minutes of pressure cooking, prepare cream sauce on stove. In a medium saucepan, cook butter over medium heat until melted. Whisk in flour until combined, and cook for 1 minute. Gradually add in the milk, and whisk until combined. Continue cooking, stirring frequently, until the mixture nearly comes to a simmer and has thickened. (It should be very thick.) Add cream sauce and kale or spinach to soup, and stir gently until combined. Season with salt and pepper (and extra Old Bay Seasoning, if you would like) as needed. Serve warm. Or transfer to sealed containers and refrigerate for up to 4 days.