function handlePassword() {
  const passwordRegexRules = /^(?=.*\d)(?=.*[a-z])(?=.*[A-Z])(?=.*[a-zA-Z])(?=.*[@$!%*?&])[A-Za-z\d@$!%*?&]{8,}$/
  const isPasswordValid = passwordRegexRules.test(password)

  if (!isPasswordValid) Alert.alert('Invalid password. Password must contain at least one uppercase letter, one digit, one special character and be 8 charachters long')
}

<TextInput 
  textContentType="password" 
  secureTextEntry 
  value={ password } 
  onChangeText={ setPassword } 
  onBlur={ handlePassword }
>
  Senha
</TextInput>