In a large skillet over medium-high heat, add 2 tablespoons of avocado oil. Working in batches if needed (use two skillets if you have them), brown the beef cubes on all sides — about 3–5 minutes per side. It is important that the beef browns rather than boiling in its own juices, so don't crowd the pan.
In the same skillet, add the remaining tablespoon of avocado oil. Add the chopped onions and pressed garlic. Use a silicone spatula to scrape up the browned bits from the bottom of the pan as the onions cook. Add the balsamic vinegar to deglaze.
Stir the tomato paste into the onion mixture and cook for an additional minute, until the paste darkens slightly.
Add the onion-tomato mixture and the browned beef to the Instant Pot. Stir to combine. Add the bone broth, bay leaves, thyme, salt, and white pepper. Stir again.
Set the Instant Pot to Pressure Cook on High for 35 minutes. Once the cooking time is complete, do a Quick Release.
Add the cubed butternut squash on top of the stew. Set the Instant Pot to Pressure Cook on High for 2 more minutes. Once complete, do a Quick Release.
In a small bowl, whisk the cornstarch and water together to make a slurry. Add the slurry to the stew and stir to combine. Set the Instant Pot to Sauté mode and cook for an additional 2–3 minutes until the stew thickens.
Serve alone or spooned over white rice.