Unity has lots of resources online and is a great choice for many beginners. Another popular engine is the Godot engine. It's a lot newer which means less resources, but it's also completely free and open source and has been growing in popularity recently. You might also wanna look at a game framework instead of an engine as you'll learn more about the ins and outs of game development. Some good ones are monogame, libGDX, and SFML.