Put your Instant Pot on the sauté setting or add some oil to a frying pan if you prefer to saute on the stove top, add oil and fry the onion for a few minutes until it is translucent.
Add the chorizo (if using) and chicken and sauté for a few more minutes until the chicken has browned.
Add the garlic and cook for 1 minute until fragrant.
Add the rice and sauté for a couple of minutes until the grains are hot to touch.
Pour in the white wine if using and let it reduce for a few minutes. (note 1)
Add the paprika, saffron threads, and balsamic vinegar, pour on the chicken stock and stir.
Set the Instant Pot to high pressure for 4 mins and do a quick release when the cooking time is up.
Add smoked or sea salt to taste.
Turn the Instant Pot to sauté mode and stir in the shrimp and cook for a couple of minutes until they are opaque. (Note 4)
Stir in the lemon juice and serve immediately.