Turn on a multi-functional pressure cooker (such as Instant Pot®), select Saute function, and add oil. Add onions to the hot oil and cook until soft and translucent, 2 to 3 minutes. Remove onions to a plate. Add beef to the pot and cook and stir until seared on all sides, 3 to 5 minutes. Mix in garlic and thyme and cook for 1 more minute. Pour in 1 cup beef broth to deglaze the pot, scraping off all the browned bits. Cancel Saute function.

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Mix in cooked onions, remaining 3 cups beef broth, mushrooms, and Worcestershire sauce. Close and lock the lid. Select High pressure according to manufacturer’s instructions; set timer for 15 minutes. Allow 10 to 15 minutes for pressure to build.

Release pressure using the natural-release method according to manufacturer’s instructions, for 5 minutes.Release remaining pressure carefully using the quick-release method, about 5 minutes. Unlock and remove the lid. Stir in egg noodles and mix to combine.

Close and lock the lid. Select High pressure according to manufacturer’s instructions; set timer for 5 minutes. Allow 10 minutes for pressure to build.

Release pressure carefully using the quick-release method, about 5 minutes. Unlock and remove the lid. Stir in sour cream. To thicken the sauce (if too thin), transfer 1/4 cup broth mixture to a small bowl and mix with cornstarch; add back to pot, stirring slowly until combined. Season with salt and pepper.