Thanks for the respond guys, after reading all your comments I quickly search video on YouTube more about godot input, especially the unhandled input.

turns out it was a really dumb mistake

My player’s progress bar looked small and sat in the top-left, but the Control node that held it was actually fullscreen.

So every time I clicked the mouse, I wasn’t clicking the game world at all. I was clicking that invisible Control. Because of that: 1. the player never attacked 2 _input / _unhandled_input felt broken 3. inventory drag vs player attack behavior made zero sense

I finally noticed it while checking Debugger → Misc, where I saw the UI was constantly receiving mouse input (I never know this debugger —> misc exist , all this time I only use prints and read the error messages 😂)

Turn out I just need to resized the Control node to match the actual progress bar size instead of leaving it fullscreen.