How to make it more 'Open World'?

Hey there, I'll try to make this as clear as I possibly can.

I've been reading the supplied modules from the GM's pack and the guidebook, and I can't help but feel as though they're a little 'on-the-rails'.

I'm very new to tabletop games, and I've admired them -- D&D in particular -- because it feels like, with enough preparation, the players could go anywhere and do anything.

Does The Expanse offer the sort of universe to be able to do that? If so, how can it be achieved? Does it make sense to have this kind of expectation of myself as a GM?

Let me know what you think.