Combine 2 tablespoons arrowroot powder, garlic, onion, salt, and seasoning in a quart-sized resealable bag. Add beef stew meat and toss to coat.
Turn on a multi-functional pressure cooker (such as Instant Pot®) and select Saute function. Add butter and olive oil and allow to get hot. Add meat and cook until browned on all sides, in batches if necessary, 5 to 10 minutes per batch. Add mushrooms and stir to combine. Mix in beef broth, vinegar, and tomato powder. Cancel Saute function.
Close and lock the lid. Select high pressure according to manufacturer's instructions; set timer for 12 minutes. Allow 10 to 15 minutes for pressure to build.
Release pressure using the natural-release method according to manufacturer's instructions, about 20 minutes. Release remaining pressure carefully using the quick-release method, about 5 minutes. Unlock and remove the lid.
Ladle 1/4 cup liquid into a small bowl and blend in 1 teaspoon arrowroot powder to make a slurry. Pour slurry into the pot; stir to incorporate. Select Saute function and cook until liquid starts to thicken, 3 to 5 minutes.