This is the root of a Sudoku game, in which we find two projects:
Backend
A Sudoku game backend, serving as a game engine. This contain no graphics at all. Just game logic. It is created as a SPM (Swift Package Manager) package, named "SudokuEngine" and placed in the folder "Backend".
Frontend
A SwiftUI iOS app serving as the UI (User Interface, a.k.a. "frontend") to the game. This is an ordinary Xcode project and thus contains a *.xcodeproj file.