Select the Sauté setting and heat the oil, butter, shallot, and garlic for about 4 minutes, until the butter is melted, the shallots are softened, and the garlic is bubbling but not browned. Add the cherry tomatoes, thyme, and salt and sauté for about 2 more minutes, until the tomatoes are slightly softened. Add the wine, bring to a simmer, and cook for about 3 minutes, until most of the wine has evaporated. Pour in the stock and bring to a simmer. Add the mussels to the pot, discarding any that do not close to the touch, and stir to coat them in the cooking liquid.
Secure the lid and set the pressure release to Sealing. Press the Cancel button to reset the cooking program, then select the Pressure Cook or Manual setting and set the cooking time for 2 minutes at low pressure. (The pot will take about 10 minutes to come up to pressure before the cooking program begins.)
When the cooking program ends, perform a quick release by moving the Pressure Release to Venting. Open the pot. Spoon the mussels into a large, shallow serving bowl, discarding any that failed to open. Pour the cooking liquid over the top.
Sprinkle with the parsley and serve right away, with the bread on the side for soaking up the cooking liquid.