How much programming experience do you have? You might want to start extra small with some games that are just played in the terminal, like tic tac toe, battleship, and hangman to practice good object oriented programming in a small project before you move on to Unity or Godot. You really need to understand object oriented programming well because Unity has some very complex classes, you are expected to understand inheritance, and so on.

When you do start with Godot or Unity start with a Mario clone, keep it really simple and finish the project.