On Instant Pot, press Saute and wait until display says Hot. Sprinkle roast with a bit of salt and pepper on all sides and add oil to Instant Pot. Sear roast on all sides for about 2 minutes per side. Remove onto a plate.
Meanwhile, in a medium bowl, combine beef broth, soy sauce, Worcestershire sauce, onion powder, garlic powder and thyme. Whisk and set aside.
Add a bit more oil and onions. Saute for about 5 minutes, stirring just a few times. Press Cancel. Add roast on top and pour beef broth mixture over it.
Close the lid, turn valve to Sealing and press Pressure Cook on High or Manual button for 1 hour. After let Instant Pot release pressure naturally, takes about 30 minutes.
Prep and Assemble the Sandwiches:
While roast is cooking, preheat large skillet on medium-high heat and add oil. Add onion and bell peppers, sprinkle with a bit of salt and pepper, and saute for 5-7 minutes or until softened and caramelized a bit. Set aside.
At same time, cut buns almost through but still attached and butter each side on the inside. Place on a large baking sheet and broil open faced just until golden brown.
Shred meat with 2 forks right in Instant Pot. Using tongs, scoop some meat while pressing on it to remove most juice and place on one side of the bun. Cover with 2 slices of cheese overlapping. Place sauteed onion and pepper on the other side. Divide meat and veggies evenly among all buns.
Place sandwiches under the broiler but on a middle rack and bake just until cheese has melted. Remove from the oven.
Place open faced or folded on a plate. Ladle au jus from Instant Pot into small ramekins and serve with each sandwich. Best served hot immediately.
Notes
Store: Refrigerate roast leftovers in an airtight container for up to 5 days.
Freeze: Freeze in an airtight container for up to 3 months. Thaw in the fridge overnight.