Turn on a multi-functional pressure cooker (such as Instant Pot(R)) and select Saute function. Add olive oil and warm for 1 to 2 minutes.
Season chicken thighs with salt. Place chicken skin-side down in the oil. Cook until skin is golden, 4 to 6 minutes. Slide a spatula underneath several times to prevent skin from sticking to the pot. Turn and cook until other side is lightly browned, 2 to 3 minutes. Transfer chicken thighs to a plate.
Add sausage, onion and red pepper to the pot. Saute until onion is softened, about 3 minutes. Stir in garlic and cook until fragrant, about 1 minute. Add rice, paprika, turmeric, cayenne and saffron. Stir constantly until spices are aromatic and rice becomes shiny.
Pour in sherry and cook until absorbed, about 1 minute. Cover ingredients with chicken stock. Scrape any browned bits off the bottom of the pot. Turn off Saute setting and place chicken thighs on top of the rice. Turn pressure regulator to sealing position; select Manual and set cooking time for 12 minutes at high pressure. Allow 10 to 15 minutes for pressure to build.
Release pressure using the natural-release method for 10 minutes according to manufacturer's instructions. Turn pressure regular to 'venting' and release remaining pressure. Remove lid, take out chicken thighs and add tomatoes and peas. Mix well.
Switch to Saute mode and cook until liquid is mostly evaporated, 3 to 5 minutes more. Top each serving of rice with a chicken thigh.