The reason why no keyboard events showing up in your “Input” field might be your language settings for UE4 editor.
If you are using Chinese as your default UE4 language, you might find “输入” together with “Input” in all the action list. However, you should find keyboard events as"键盘事件" in “输入”, rather than “Input”.
It’s recommended to set English as default language to keep the uniform standard.