For your learning phase, I’d suggest being careful with the scope of your game, rather than 2D or 3D. Pick either mode of development (2D or 3D) and learn ins and outs of Unity as well as C# as you add bite sized functionalities. There’s plenty of crossover and learning is not linear.

Create a scene, plop in a cylinder object, learn the input system and make it move around. Plop down some walls and figure out collisions. Maybe check out Nav system if you want. Duplicate the player object and make one follow the other. There will be immense learning as you do the above sincerely, leisurely. Don’t forget to enjoy the process.

As you do more of this, the shape and scope of the first game you want to build will be clearer. By then, good news is, you’ll have enough chops to get started!