Place the lid on the pot and set the steam release knob to the Sealing position. Then press the Pressure Cook/Manual button, or dial and then the + or - button or dial to select 30 minutes.
While the meatloaf and potatoes are cooking, mix up the topping by adding the ketchup, BBQ sauce, mustard, and brown sugar, if using, in a bowl. Set aside.
When the cook cycle ends, turn off the pot and let it sit for 10 minutes (10 minute natural release). Then turn the steam release knob to the Venting position and do a Quick Release of the remaining steam.
When the pin in the lid drops down, open it and get a meat thermometer and take the temperature of the meatloaf. Beef should be 160°, turkey should be 165°.If it isn't done, put the lid back on and set time for another 10 minutes and cook it longer (I have never had this happen, but people may put in different ingredients, or may be at a higher altitude, which will affect cooking time). Get a turkey baster and a baking sheet pan.
Use the turkey baster to suction out most of the drippings so that when you lift the meatloaf out of the pot, hot drippings won't spill on you. Just put them in a coffee cup or a bowl.
Lift the foil with the meatloaf on it out of the pot and onto the baking sheet pan. Spread the topping on the meatloaf and put under the broiler at 425° until it's caramelized to your liking.