Heat the oil in a large pot over medium heat. Swirl in the flour and continually stir until the flour is incorporated, forming a roux. Constantly stir the roux for 20-30 minutes (or longer), ensuring nothing sticks to the bottom of the pot, or it may burn. The roux will darken to a peanut butter color to a light chocolate color. *See my NOTES above on making a roux.
Add the onion, peppers, garlic and okra. Stir the mixture often, about 5 minutes, until the okra is no longer slimy.
Stir in the beer, seafood stock, Cajun seasonings, cayenne pepper, salt, thyme, bay leaves, Worcestershire and hot sauce.
Bring the pot to a quick boil, then reduce the heat to low and simmer for at least 1 hour. 1.5-2 hours will develop more flavor.
When nearly ready to serve, add in the shrimp, fish, crab and oysters* (See my NOTES above about your seafood options). Cook another 10 minutes, or until all the seafood has cooked through.
Stir in the fresh parsley.
Serve the seafood gumbo into bowls with rice and top with fresh chopped parsley, spicy chili flakes, spicy chili oil, and extra hot sauce if desired.