Choose any game that's already made, and remake it and add your own twist to it. There isn't really a "bad" project for a person to start off with except for things way above their skill level like making a game engine, making an operating system, etc. Though even those types of projects are all based off of how much time and effort you are willing to put into it. And of course, like all programming, you will need a lot of patience.
As a quick quibble, most people in the world do not finish learning C++. It just doesn't happen. Keep reading, keep practicing.
Try starting with some simple game for which the coding seems "obvious" to you. For example if you did not write Tic-Tac-Toe while learning C++ (hope you did) - start with it.
Perhaps it would be worth starting with bare console implementation if you feel yourself not strong enough - like this:
Make it working for two human players, preferably with cute graphics, then add a computer player for Xs or Os.
Starting with a simple (trivial) game will allow you to get hold on all secondary things - like organizing menus, restarts, notifications, managing your code etc.
After it you will feel yourself far more experienced and it would be far easier to select further path.