the title prop of a button must be a string - react native

I think you have closed the Button tag too early.

<Button
  style={{fontSize: 20, color: 'green'}}
  styleDisabled={{color: 'red'}}
  onPress={() => this._handlePress()}> // <-- closed tag here
  title="Press Me"
</Button>

Just close the tag after the title attribute

<Button
  style={{fontSize: 20, color: 'green'}}
  styleDisabled={{color: 'red'}}
  onPress={() => this._handlePress()}
  title="Press Me"
>
  Press Me
</Button>

Button name should be written with title keyword

Example :

<Button
  style={{fontSize: 20, color: 'green'}}
  styleDisabled={{color: 'red'}}
  onPress={() => this._handlePress()}
  title="Press Me"
>
</Button>

title="Press Me" inside Button tag