“Gravel Bike” is a broad term that can cover everything from an “All Road” bike (basically an endurance road bike that takes big tires… like 38s), to bikes bordering on drop bar MTBs.
Sort of like the term “Mountain Bike”. It covers a wide range of bike types.
What you should get depends on what kind of unpaved surfaces you are dealing with, how much time you spend on/off pavement, what that pavement is like and how much you care about performance on pavement vs off-pavement.