By design, i mean structure.
It will be easier to explain with an example :
In the first book of the Pathfinder Kingmaker campaign, the party has to explore and take control of a region no kingdom has yet been able to annex. They also protect an outpost from the bandits and explore the region hex by hex to finally beat the bandit lord which conclude the first book.
The structure is simple and effective : explore and fight until the region is rid of its threats.
In Forbidden Land, the campaign is really open and the players do whatever they want (almost) until bits by bits being led to discover the “main quest”. The campaign conclude when the party beats the main threat in the region.
The design of this campaign (The Raven’s Purge) revolve around adventure sites and events that leads to a final adventure site.
I don’t know if this is well explained but i’m seeking variation of those open-world ttrpg campaign to use them as framework for an AI to generate content for the GM to edit or run as is.