You're quoting this article, but you're misunderstanding it:

https://phys.libretexts.org/Bookshelves/University_Physics/U....

This is calculating the gravitational potential between two point masses. In other words, the potential energy if both masses were singular points at a distance from each other.

I was quoting the potential energy differential between being 100km over the ground, and on the ground. This is 98 MJ for a 100kg object, and that's what you have to cancel out to land back on Earth. The total gravitational energy of that object to the Earth's centre is more like 6300 MJ, but that's a meaningless number.