Heat a dry frying pan over medium-low heat.
Toast the dry spice aromatics (cinnamon, star anise, cardamom, fennel, coriander, cloves) in the frying pan until slightly fragrant.
Place the toasted spices over top the cheesecloth.
Next, put the onion and ginger in the frying pan and let them char until blackened. Use a pair of tongs to flip and char the other side.
Place the blackened onion and ginger into the cheesecloth. Tie the cloth with a piece of twine. Set the spice bag into the Instant Pot liner.
Add the cleaned beef bones and beef tendon into the Instant Pot. Cover the bones with enough water, up until right before the MAX line.
Make sure the exterior of the Instant Pot liner is dry and place it into the Instant Pot cooker. Place the lid on and close securely.
Ensure the steam valve is set to sealing.
Set the cooking program to Meat/Stew and High Pressure. It will automatically be set for 35 minutes. (Note: if you want the tendon to be a little softer, do a Manual setting of 50 minutes on High Pressure).
In the meantime, prepare the rice noodles by filling a large pot of water and bringing it up to a boil. Blanch the noodles for about 2 minutes and drain under cold running water. The hot soup broth will continue to cook the noodles further.
Assemble portions of the noodles into bowls.
When the Instant Pot beeps, it will start to depressurize (takes about 15 minutes). Once the float valve comes down, carefully open the lid, remove the beef meat and bones.
Portion out the meat into the noodle bowls.