Required fields at checkout not be marked?

Hello,

I have set mandatory fields in the backend for some input fields for the delivery address (see screen).
However, these mandatory fields will not be marked if they are left blank and the submit button is clicked.
The form will not be submitted, but the user will not be notified of the missing entries, e.g. with red border around the empty input field, attentive.

Where can i customize that? And in which file can I find the individual input fields for the delivery address?

Thank you and best regards
F.