TL;DR: No one is telling you that you can't add okra. I'm just telling you that it is not required.

NOLA isn't the end-all to Louisiana food. New Orleans is its own thing. Cajuns come from the Acadiana region of Louisiana. Another common misconception is that we're all from New Orleans.

Short history of Cajuns: In the Seven Years War, the UK wanted what was known as New France, the maritime provinces of Canada. They attempted to get the Acadians to swear an oath to the king of England. The Acadians refused and were dragged into the war in what became known as the French-Indian war as the First Nations peoples fought alongside the French and early French settlers known as the Acadians (Acadien en Francais). The Acadians, after the war, were dispersed, known as the Great Expulsion.

Eventually, the Acadians arrived in Louisiana. They weren't welcomed in New Orleans where there were already French immigrants. So they settled the lands west of NOLA in a region now called Acadiana.

The word Cajun is a bastardization of Acadien, ah-cad-yan.

The Cajuns, the Creoles, and the Native Americans developed food Louisiana is known for and over time, those dishes evolved into what they are today. One notable example of a dish with a lot of Native American influence, besides gumbo, is maque choux, a French bastardization of the Native American word for it.

Fast forward 150 years and you have two separate food cultures that blend together at times, for example a courtbouillon and sauce piquant.

There is a misconception that okra is absolutely required in a gumbo, a misconception I see pop up a lot on Reddit. It doesn't matter the etymology of gumbo any more. It no longer stands true if, and that's a big if, the original word for it is from the African word for okra. You can put what you want in gumbo but okra is not a requirement. Requirement means: a thing that is compulsory; a necessary condition. It is not necessary to include okra in a gumbo. You can add it if you want. It is not required.