For example, when you play the game deadmaze, the first thing that shows up is a window filled with the login boxes, along with a background painting and other stuff. Does that generally have a specific tech name within the gaming context? Thanks in advance!
The splash screen usually does not allow user interaction and serves only as an indicator that the game is launching. The login screen allows a user to log in. The main menu is usually a screen that allows the user to choose a game mode or level before beginning the real action of the game.
My hunch is that you are looking for login screen, because you specifically mention login boxes.