Viewmodel.kt

    val isSubmitEnabled: Flow<Boolean> = combine(_firstName, _password, _userID) { firstName, password, userId ->
            val regexString = "[a-zA-Z]+"
            val isNameCorrect = firstName.matches(regexString.toRegex())
            val isPasswordCorrect = password.length > 8
            val isUserIdCorrect = userId.contains("_")
            return@combine isNameCorrect and isPasswordCorrect and isUserIdCorrect
        }