Set the Instant Pot in saute mode. Add the 3 tbsp of oil and, when the oil is hot, add the bay leaf chopped onion and garlic. Add the salt and sugar as well. Water will ooze out, and it's normal. Saute until the onion turns soft and tender or for about 3 to 4 minutes. Now turn off the Instant Pot. Turning it off after sauteing onion helps to prevent the burn signal in the newer Instant Pot models.
Now spread the eggplant and then add the celery and olives on top.
Next, add the bell peppers, tomatoes, capers, raisins, Italian seasoning, red wine vinegar, black pepper, and chili flakes. Do not mix.
Close the Instant Pot. Make sure the vent is in the sealing position. Select manual/pressure cook and set the time to 3-minutes at high-pressure mode. When the cooking is complete, naturally release the pressure.
Carefully open the lid. Now add some fresh basil, gently mix the caponata. Check for seasoning and adjust at this stage. If you add some seasoning, simmer it for a couple of minutes and turn off the heat. Serve it with pasta, or with bruschetta, or as is.
Adjust the salt, spices, and sugar to your taste preference.
You can use fresh red bell peppers and fresh tomatoes instead of canned ones. Also, black olives work too.
As we are making it in Instant Pot, it's won't be thick like a relish. Eggplant oozes out water when we pressure cook, so it's more like a stew. When serving on top of bread, drain the liquid and serve.