Are we thinking about a single player game, or multiplayer?
Videogame, something physical (like a card or board game), or is either ok?
Proposal is, at the core, about one person asking a question, and the other responding. The asker could consider getting a “yes” to be a victory condition, and a “no” to be failure. “Maybe” could be an opportunity to try again. For the person being asked, there isn't any inherently obvious victory condition.
Proposals often involve elaborate romantic plans or gestures, choosing rings or other gifts, etc. These could possibly be elements in the game.
Sometimes, people plan a proposal and then things go wrong: the weather isn't as expected, a venue is closed, a meal is incorrect, there is a clashing event and makes a loud party atmosphere where a quiet romantic one was expected, etc. These sort of events could be potential obstacles to overcome.