Turn on a multi-functional pressure cooker (such as Instant Pot) and select Saute function. Once the panel reads HOT, add butter, shallot, and garlic. Cook and stir until fragrant, about 2 minutes. Add rice and cook, stirring, 1 minute more. Add wine and quickly deglaze by using a wooden spoon to scrape the brown bits from the bottom of the pot. Add 1 1/2 cups chicken broth, salt, and pepper. Stir to combine. Cancel Saute mode.
Close and lock the lid. Select high pressure according to manufacturer's instructions; set timer for 12 minutes. Allow 10 to 15 minutes for pressure to build.
Release pressure carefully using the quick-release method according to manufacturer's instructions, about 5 minutes. Unlock and remove the lid. Select Saute function.
Stir in shrimp and the remaining 1/2 cup of broth. Cook, stirring occasionally, until the shrimp are opaque, 3 to 5 minutes. Stir in Parmesan cheese until melted, then add parsley. Serve immediately and sprinkle with Cajun seasoning to taste.