Set a large Dutch oven over medium heat and add the chopped bacon. Cook, stirring now and then, until the pieces are browned and crisp, about 6 to 8 minutes.
Lift the bacon out with a slotted spoon and set it on a paper towel. Pour off all but about 1 tablespoon of the bacon fat, leaving that behind for flavor.
Add the butter to the pot with the reserved bacon fat and let it melt. Stir in the diced onion, celery, and red bell pepper and cook over medium heat until softened and just starting to color, about 5 minutes. Add the minced garlic and cook for 1 more minute, stirring so it does not scorch.
Sprinkle the flour evenly over the vegetables and stir constantly for 1 to 2 minutes so the raw flour taste cooks out and the mixture looks like wet sand.
Pour in the seafood stock a little at a time, whisking after each addition to keep it smooth. Keep whisking until the liquid is lump-free and starts to thicken slightly.
Add the cubed Yukon Gold potatoes, Old Bay, smoked paprika, and thyme. Bring the pot to a gentle simmer, then lower the heat to keep it there. Cook uncovered for 15 to 18 minutes, until the potatoes are fork-tender, stirring occasionally so nothing sticks to the bottom.
Stir in the corn kernels, heavy cream, and whole milk. Add the dry sherry now if you are using it. Warm everything gently for about 5 minutes, keeping the heat low so the chowder never boils.
Slide the raw shrimp into the pot and stir to submerge them. Simmer for just 3 to 4 minutes, until the shrimp turn pink and opaque and curl loosely. Pull the pot from the heat as soon as they are done so they stay tender.
Taste and adjust with salt, black pepper, and a few dashes of hot sauce if you like heat. Stir most of the crisp bacon back in, saving some for the top. Ladle into bowls and finish with the reserved bacon, chopped parsley, and sliced green onions.