Season the oxtails with the kosher and garlic salts and the red pepper flakes. Heat the olive oil in the stovetop pressure cooker over medium-high or use the brown function for the electric pressure cooker. Add the oxtails and dried spices and herbs and brown on all sides, about 3 minutes. Add the onion and garlic. Pour the beef broth over the oxtails. Give it a good stir and cook for 2 to 4 minutes. Cancel cooking for the electric cooker, and close the lid.
Stovetop: Set to high pressure (15 PSI) and cook over high heat for 25 minutes total.
Electric: Set to high pressure (10–12 PSI) and 30 minutes.
While the oxtails are cooking in the pressure cooker, cook the yuca in a separate pot on the stove. Add enough water to cover the yuca. Season with salt to taste and gently stir. Cook over medium-high heat for 25 minutes, or until the yuca is mostly tender but not mushy. Strain and set aside.
When the oxtails are done, turn off the heat but keep the stovetop cooker on the range or cancel cooking for the electric cooker. Allow the pressure to release on its own (natural-release). If the pressure is not fully released after 10 minutes, apply auto-release. When all of the pressure is out, add the yuca and the Swiss chard. Cover the cooker but don’t apply any pressure. For the stovetop cooker, cook over medium heat for 7 minutes; for the electric cooker, reset to the sauté function and 9 to 10 minutes; or cook until chard is tender but not wilted.
Evenly distribute into individual bowls. Garnish each serving with a handful of julienned Swiss chard stems.