Rinse split peas, cover with water, and soak for 1 hour. Drain.
Set Instant Pot to Sauté. Add butter or oil, minced onion, and diced carrot. Cook for 4–5 minutes until softened. Add garlic during the last 30 seconds.
Turn off Sauté. Add drained split peas, ham, broth, pepper, thyme, and bay leaf. Stir well, scraping the bottom of the pot.
Secure the lid and set the valve to Sealing. Cook on High Pressure for 12 minutes.
Allow pressure to release naturally for 15–20 minutes, then carefully release any remaining pressure.
Remove bay leaf and stir until creamy. If the soup is too thin, turn on Sauté and simmer uncovered, stirring frequently until thickened.