Some players are running into an issue where their Xbox One controller becomes unresponsive. This can occur for the first time at the Title Menu or in a game when opening inventory or menus.
Title Menu: Restart Grounded or plug in a keyboard to get past the welcome message.
In-game: Restart Grounded.
Some players have also mentioned that if a second controller is connected, it may need to be turned off as it can take over some controls.