Step 1
Turn on a multi-functional pressure cooker (such as Instant Pot®) and select Saute function.
Step 2
Combine garlic salt oregano and thyme in a small bowl. Sprinkle over chicken thighs skin-side up.
Step 3
Add grapeseed oil to the pressure cooker when it says 'hot.' Sear chicken thighs skin-side down until no longer pink in the center and juices run clear 2 to 3 minutes per side. Continue in batches with any remaining chicken thighs. Transfer to a plate.
Step 4
Drain any remaining oil in the pressure cooker. Add onion and garlic and cook until softened about 1 minute. Pour in chicken broth scraping the bottom of the cooker to ensure brown bits are incorporated.
Step 5
Turn off the pressure cooker. Place chicken thighs back into the cooker skin-side up overlapping if needed.
Step 6
Mix Dijon mustard and maple syrup together in a small bowl. Pour over chicken thighs. Close and lock the lid. Select high pressure according to manufacturer's instructions; set timer for 15 minutes. Allow 10 to 15 minutes for pressure to build.
Step 7
Release pressure using the natural-release method according to manufacturer's instructions 10 to 40 minutes. Transfer chicken to a plate.
Step 8
Add mushrooms to the pressure cooker. Whisk heavy cream and cornstarch together in a bowl; stir into remaining liquid in the pressure cooker.
Step 9
Turn on the multi-functional pressure cooker and select Saute function. Let sauce simmer whisking often until thickened 5 to 7 minutes. Serve with chicken thighs.