Heat oil in the cooker. Add sliced onions and stir to coat onions thoroughly with oil. Stir frequently when cooking, until onions are reduced, about 15 minutes.
Add the sugar and vinegar and continue sautéing, occasionally stirring, until the onions are caramelized, about 15-20 minutes.
Add the wine, stir, and let it evaporate. Add beef broth, thyme, and bay leaf, scraping the bottom of the removable pot to loosen browned bits.
Close and lock the lid of the cooker and set the regulator knob to PRESSURE. Set the timer for 5 minutes. The level of pressure should be on the HIGH setting.
Quick-release the pressure when the function has ended. Remove the lid away from the face. Use the warm function to keep the soup hot while preparing the baguette slices.
Preheat oven to 400° Arrange the baguette slices in a single layer on a baking sheet and bake until the bread is dry, crisp, and golden at edges; about 7 minutes Set aside until ready to use.
When ready to serve the onion soup, adjust oven rack to the upper-middle position; turn on the broiler. Set soup bowls on a baking sheet and fill each with about 1 cup of soup. Top each bowl with a toasted baguette slice and divide Swiss cheese evenly among the bowls.
Place the bowls into the oven, about 5 to 6 inches from the broiler and broil until cheese is brown and bubbling; about 2-3 minutes.