Add 6 tablespoons of oil to a heavy bottomed pot over medium high heat. Heat for about 5 minutes until very hot.
Add the okra to the hot oil and fry for 2-3 minutes, stirring occasionally. Remove okra from the pot, leaving the oil behind.
Add the remaining 2 tablespoons of oil to the pot. Reduce the heat to medium.
Add the flour. Stir together and a thick paste will form. Continue to cook, stirring slowly and constantly for 20 minutes until the roux reaches a milk chocolate brown color.
Add the onion, green pepper, celery and 2 tablespoons of cajun seasoning to the roux. Stir constantly and cook for 2-3 minutes.
Add the garlic, bay leaves, and remaining cajun seasoning and cook 1 minute more.
Add the broth, thyme, apple cider vinegar, and mushrooms. Stir well to incorporate all of the flour with the liquid.
Add the okra back to the pot. Bring to a simmer and cook uncovered for 30 minutes. Stir occasionally to make sure no flour is stuck to the bottom of the pot.
Skim off any foam or oil that gathers on the surface of the gumbo and discard.
After 30 minutes of cooking, add the beans and sausage. Cook for an additional 30 minutes.
Remove the bay leaves and thyme sprigs from the pot before serving.
Serve with white rice and garnish with fresh parsley, green onions and file powder.