I like to keep track of my games that I have completed, with most of the games it is pretty easy. When the credits roll, I consider them beat, there are a few exceptions of course like Nier, Resident Evil 2 etc. What I struggle with are fighting, racing games and 4x games. I enjoy these genres, but I don’t know what is “satisfactory” amount that would make me think that I played these games to completion.
Some examples:
- Guilty Gear Strive (or any fighting games that are not Mortal Kombat, injustice or SF6)
- Civilization 6
- Project Cars
As others have said, the best answer is “whenever you want”, though obviously sometimes you don’t know when that is! If you need a little more structure you can see what the game presents to you as all the things you can do, for instance by completing all the achievements. Remember that sometimes the final achievements are ludicrously difficult, so if you’re not enjoying it just call it a day!