It’s basically like you check out the destination branch and cherry pick your changes on top of it.

I don’t know if there is a functional difference between a merge and a rebase assuming your git history is reasonable, but rebasing makes the history so much easier to follow. Every commit only has a single ancestor, commits are generally better structured because devs where I work tend to squash and rebase.

A lot of the free games also have DLC for sale. If you play the free game and enjoy it, odds are that it is cheaper to get the DLC on epic instead of buying the game and dlc on steam. No idea how often that works out for epic, but it’s one way they could make money back from free games.