Select [Saute] to preheat the pressure cooker on saute mode. When the word “Hot” appears on the display, add cooking oil to heat until shiny and smoking. Sear the oxtail on the hot oil, turning every 1-2 mins to brown all sides.
Remove the oxtail and set aside. Saute the onions and garlic in the Instant Pot®.
Deglaze the pot by pouring 1 cup of beef broth and scraping the bottom of the pan with a wooden spoon until no food bits are stuck.
Return the oxtail and tripe and pour the remaining 3 cups of beef stock. Close the lid and set the steam release handle to the Sealing Position. Select [Pressure Cook] and [Pressure Level] to High then use the [+] or [-] buttons to set the time to 45 mins.
Once done, turn the pressure release valve for Quick Release of pressure. Either use mittens or a wooden spoon to do this. Open the lid and transfer oxtail and tripe into a container.
Stir in the fish sauce, peanut butter, and annatto oil. Let it thicken then add the vegetables. Press [Cancel] and then [Saute]. With the lid off, continue cooking the vegetables until all are soft and tender.