How do I make a game in 2 separate projects?

Hi

I want to make a "game" that is just part of a larger game, sort of like a DLC, but packaged with the game. How do I do this with 2 different projects?

You would not. A dlc is part of the same project, as dlcs normally do not work on their own. The base game is required. You would probably just export two versions of the same project, one with the dlc content and one without.

to clarify, if you exported them together in one installer file, would that change anything? I am just trying to figure out if one project would be able to interact with another, and how that would work. however, thank you for telling me this.