As you can see the code from my Visual Studio Code, it won't let me type within the text input if I render the code

The onChange event on line 36 invokes (updateInput) function. Which doesn't exist or declared inside the component, if you sent it as a prop use :
this.props.updateInput(_params_)
Otherwise declare the function inside the component in order to make the event work properly.
That's because <input /> has constant value, so you need to change value to defaultValue.
<input
type="text"
placeholder="Insert text"
defaultValue={this.state.newItem}
onChange={() => {}}
/>