Beef Tips with Mushrooms (Slow Cooker or Instant Pot)

Ingredients:
1 1/2 pounds beef stew meat (such as chuck or round), cut into bite-sized pieces
1 cup beef broth
1/2 cup red wine (optional, can substitute with additional beef broth)
1/2 cup soy sauce
1/4 cup Worcestershire sauce
1 tablespoon tomato paste
2 tablespoons olive oil
1 medium onion, diced
3 cloves garlic, minced
1 cup sliced mushrooms (button or cremini)
2 tablespoons cornstarch (optional, for thickening)
2 tablespoons water (optional, for thickening)
Salt and pepper to taste
Fresh parsley, chopped (for garnish)