On a 6-quart Instant Pot, select More/High Sauté. Add the butter and melt. Add the onion and garlic, then cook, stirring occasionally, until the onion begins to soften, about 5 minutes.
Stir in the miso and cook until lightly browned, about 2 minutes. Add the vermouth and cook, stirring, until almost fully evaporated, about 5 minutes.
Add 3 cups water and whisk until the miso dissolves. Stir in the mushrooms and bring to a boil, then distribute in an even layer.
Press Cancel, lock the lid in place and move the pressure valve to Sealing. Select Pressure Cook or Manual; make sure the pressure level is set to High. Set the cooking time for 5 minutes.
When pressure cooking is complete, quick-release the steam by moving the pressure valve to Venting. Press Cancel, then carefully open the pot.
Select More/High Sauté. Bring the mixture to a boil and add the pasta. Cook, stirring often, until the pasta is al dente and the sauce clings lightly, about 10 minutes.
Press Cancel to turn off the pot. Stir in the thyme and lemon juice, then taste and season with salt and pepper. Transfer to a serving dish and sprinkle with the parsley and pecorino.
