Why game developing is too hard? even when i do a tutorial from YouTube? (Note: I use Godot 4)
Because computers are complex machines and games use a wide array of their abilities. Games are some of the most complex software in the world.
Learning how to develop any kind of software takes time and effort - games, doubly so.
Personally, I would recommend you grab some books (ideally, ones from 2023 or earlier as the game-making book market is flooded with AI slop these days) about Godot, and possibly on programming on general because gamemaking books tend to gloss over the basics. Really work through these books, type in the example code yourself and mess around with it. That's the only way to gain a structured understanding and the ability to actually do things, in my experience. A tutorial from YouTube cannot give you that.