When you use [] to bind to an @Input(), it’s basically a template expression.
The same way displaying {{abc}} wouldn’t display anything (unless you actually had a variable called abc).
If you have a string @Input(), and you want to bind it to a constant string, you could bind it like this: [myText]=" 'some text' ", or in short, like a normal HTML attribute: myText="some text".
The reason [myEnabled]="true" worked is because true is a valid template expression which of course evaluates to the boolean true.