There are hundreds of thousands of games that have been developed using Unity, and it is widely used for both 2D and 3D games across all modern gaming platforms. It is a powerful game engine that lets you build games for every modern platform. It is still an excellent technical platform for game development, despite the company’s recent behavior.
It’s essentially a simulation environment with physics, animation, and rendering built into a neat application, all of which can be easily integrated with external tools. You can make a game without a game engine, it’s just way more work, and it’s also possible to make things that aren’t games with a game engine, it just might not be the right fit.