Purchasing Using Game Codes/Keys

I have just recently started paying monthly for ea play. The only game that I play is FIFA 22 but really I want to purchase the full game. I have discovered that I can purchase using a game code/key but I don't really know much about it. And on the ea app it doesn't have an option to purchase you can only pay monthly to play FIFA 22. What I want to know is that if I use the game code/keys and I have the full game can I cancel my subscription and still have the game or...?

And can someone please explain in detail how this game code/key really works on the ea app🙏🙏