Saute the onion and carrot in 1 cup of broth for about three minutes. Use the sauté function and sauté in the instant pot. Pay attention to the bottom of your pot so that the broth does not dry out and the vegetables stick. If the vegetables stick, your pan may not press.
Add all the other ingredients: lentils, canned diced tomatoes, celery, potatoes, garlic, seasonings, vinegar and lemon juice, and the remaining four glasses of broth. Mix.
In manual mode, set your pressure cooker on high for 12 minutes.
After the vegetable soup. comes to pressure and counts down, allow a natural release for 10 minutes.
After waiting 10 minutes for natural release, continue to release pressure carefully with a long-handled spoon or similar tool. Open your pot.
Depending on how thin you like your soup. you may want to add some vegetable broth. Add salt and pepper to taste.