Also Flemish nationalism makes in no way sense. There is 0 effort from the Belgian government to oppress Flemish people. It is by far the biggest demographic group with the most spoken language. They have their own government. They are free to teach Flemish history, language and whatnot.
Then you have the historical aspect of it. I'd say the movement is strongest in the provinces of East and West Flanders. Which are historically speaking Flanders. But then you have places like the province of Antwerp, where I live, and you also have these people supporting it. Except historically speaking Antwerp, Flemish Brabant and Brussels have been part of the Duchy of Brabant. Same with Limburg but with the Duchy of Limburg.
The movement makes at least some sense in the Lille region of France, which is historically speaking Flanders. But even there it is hijacked by right wing nationalism.