The issue here is that they didn't submit a permit application for protest. It might sound weird but in Belgium you can protest all you want as long as you get a permit with an explanation where you will protest and a ball park number of people you think might come so that the city can foresee available paramedics and police officers in case of emergencies and to make streets car free so the people can protest in peace.

On occasion your permit might get denied if there already is a protest on the same day on the same place or if there just is not enough police or paramedics available

The "Freedom Convoy" didn't apply for a permit. If they would have there would have been no issues what so ever.