Select the saute mode on the pressure cooker for medium heat. Cut the bacon into small pieces and add them to the heated pot. Cook until crispy.. Transfer to a paper towel-lined plate to drain, leaving the bacon grease in the pot.
Add butter, celery, onions, garlic, salt, and pepper to the pressure cooker. Cook for a few minutes, stirring occasionally until onions are soft and translucent. Turn off the saute mode.
Add cauliflower florets and water, then stir and check that the cauliflower is submerged. Add additional water as needed. Secure and seal the pressure cooker lid.
Cook for 5 minutes at high pressure, followed by a manual pressure release.
Uncover. Add cream cheese and shredded cheddar cheese.
Use a blender or food processor to puree until smooth or to desired texture.
Taste and adjust salt and pepper as needed. Serve in bowls, optionally sprinkling with shredded cheese and sliced scallions. Crumble bacon on top.