Season the pork shoulder with salt and pepper.
Set your Instant Pot to Sauté mode. Add the olive oil and butter. Once hot, sear the pork on all sides until nicely browned.
Add the onion, celery, fennel, garlic powder, thyme, sage, lemon zest, water, and baking soda.
Seal the lid and cook on High Pressure for 20 minutes. Allow a natural pressure release for 10 minutes, then quick release the rest.
Test the pork with a fork — it should be starting to shred easily. If needed, cook for another 10–20 minutes on high pressure.
Once the pork is fork-tender, stir in the baby spinach and half & half.
Set the Instant Pot to Sauté mode again and cook for 5 minutes until the spinach is wilted and the stew is hot.
Release the pressure, remove any herb stems, and roughly shred the pork right in the pot.
Taste and adjust seasoning if needed. Serve hot!