Combine the chicken stock, tamari soy sauce, brown sugar, Chinese five-spice powder, garlic purée, ginger purée and chilli flakes in a bowl and set aside.
Turn the Instant Pot to sauté setting, add the oil to the insert and when hot, brown the pork on all sides in 2 batches (approx. 6-8 mins).
When done remove the pork and set aside.
Add the stock mixture to the Instant Pot insert and deglaze the insert in case anything is stuck on, then add the pork back in.
Cover your Instant Pot, set the vent to seal, select the manual (or pressure cook) setting and set the timer to 45 mins, and let the pork cook under high pressure until done. When done let the pressure release naturally.
Transfer the pork to a plate and shred (If the pork does not shred easily, add back into the Instant Pot and cook for an additional 10 mins on high pressure).
Optional step: Press the sauté button once more, and let the sauce simmer for 10-15 mins or until it has thickened and reduced by more than half.
Return the shredded pork to the Instant Pot, stir and serve.