Yeah, don’t try to remake an active, money-making game like TF2 with plans for releasing it…
As a corollary to what you mentioned, if you want to get a job in the games industry, the number one thing you can do is make a game. A straight remake is great for engineers or artists, and a remake with specific improvements is great for designers. And you don’t have to do anything from scratch, unless you are looking for a core engine type job. Using a game engine like Unreal and publicly available assets and libraries is fine. You also don’t ever have to release or announce your project. The important thing is that you will very quickly learn about the challenges of making a game. If you can start answering questions in an interview and talk about where you encountered challenges, how you researched solving them, etc., you will be that much closer to landing a job.