If the global flood was true and the majority of the water came from inside the earth

wouldn`t it have collapsed the earth from all the weight and void areas where the water was?...(it says the water covered the highest mountains)

Yes, that certainly would have been a possibility.

And that, among other things points to at least two other conclusions about that story:
- The whole story is a myth, designed as a metaphor to teach a lesson.
- The flood was really very localized and caused by some naturally dammed water source breaking through the containing barrier.