Whenever you export the modifiers are gone/only whatever is applied is retained.
There is an option to automatically apply modifiers that usually works.
Though it working and how long it takes to process varies greately.
Best example on that is repeating patterns.
Billions of objects will take a lot longer to merge down and export.
They probably also won’t import in the engine unless you add a triangulation modifier to it.
The engine takes a lot longer than Blender to process triangulation.