"Add new account" button is disabled

The “Add new account” button is disabled. In the dropdown showing altcoins (in the “Create New Account” section), “Litecoin” is also missing (I have by default Litecoin in Bisq)

Please notice I did not set any national currency account yet. Is this mandatory?

Do you have Litecoin as the base currency in Bisq, is that what you meant?
If you do, then you shouldn’t be able to create an altcoin account for Litecoin, as that would be handled by the Bisq’s internal wallet.