Turn on a multi-functional pressure cooker (such as Instant Pot(R)) and select Saute function. Heat vegetable oil.
Season chicken thighs with salt and pepper on both sides; add to Instant Pot(R). Cook one side at a time until both sides of the chicken are a golden brown, 3 to 4 minutes per side. Remove chicken from the pot and set aside.
Add onion and sauté for 1 minute. Add garlic and cook for 1 more minute. Pour in white wine and stir to scrape brown bits from the bottom of the pot. Stir in chicken broth and lemon juice; bring to a boil and cook until broth has reduced slightly, 2 to 3 minutes. Turn off the Sauté function.
Return chicken Instant Pot(R). Close and lock the lid. Select High pressure according to manufacturer’s instructions; set timer for 10 minutes. Allow 10 to 15 minutes for pressure to build.
Release pressure using the natural-release method according to manufacturer’s instructions, for 10 minutes. Release remaining pressure carefully using the quick-release method, about 5 minutes. Unlock and remove the lid.
Optional step: Whisk heavy cream and corn starch together in a small bowl if you prefer a thicker sauce (this will add to the net carbs of the meal, but will thicken the sauce). Leave the cream on its own if you prefer lower carbs with a lighter sauce.
Remove chicken from the pot and set aside. Select the Sauté mode and bring sauce to a boil.
Whisk in heavy cream, butter or margarine, salt, and thyme. Cook until sauce has thickened slightly, 2 to 3 minutes. Serve chicken drizzled with the sauce.