Marinate beef with salt, pepper, cumin, oregano, garlic, and vinegar for a minimum of half an hour.
Add beef mixture, butter, soy sauce, and water to the Instant Pot, cover, set to seat.
Set high pressure to 20 minutes.
Once timer goes off, press cancel, and allow to naturally release for 5-10 minutes before moving the knob to quick release.
Drain your barbacoa beef, and assemble your tacos as desired.