Select "Saute" on the Instant Pot. Allow pot to heat, it will indicate "Hot" on the display when ready.
Add olive oil, once hot add the onions. Saute until fragrant and tender, 2 minutes.
Add carrots and celery, saute until tender, 3 minutes.
Add garlic and saute until fragrant, 30 seconds.
Add butternut squash, saute for 2 minutes.
Add lentils, vegetable stock, bay leaf, salt, pepper, and thyme. I find that once you add the cooled stock the saute function turns off.
Make sure that the release valve is in the "Sealing" position.
Place the lid on the Instant Pot, turn and lock.
Press "Manual" button on the Instant Pot on high pressure, and then set the timer to 10 minutes using the "+" or "-" buttons. It will take about 10 minutes for the pot to heat and build up pressure. You will see some steam release from the lid, and then the time will start on the display.
Once the cook time is complete, use the quick-release method to release the steam by pressing "cancel" on the Instant Pot.
Use an oven mitt or towel to slowly and carefully twist the steam-release handle on the lid to "Venting" position. The initial release will spray some moisture around the pot so be careful.
Remove the lid, opening the top away from you as steam will be released from the pot.
Remove and discard bay leaf.
Use a hand immersion blender to puree the soup until smooth, or transfer to a blender and puree. Leave some pieces of vegetables and lentils whole if desired for a chunkier consistency.