Only way I can think of without javascript would be to add a custom validation that will pass if any of your top-level answer is selected.

Might be painful to set up if you have a lot of top-level answers.

Hi ​@surrogate-key ,

Forcing a response only at the top level isn't a built-in Qualtrics feature, but you can try with the  workaround with Custom Validation.Then, set a condition to display an error message if the top-level dropdown is left empty. This ensures respondents must select a top-level option while allowing lower levels to remain optional.

For your reference: https://www.qualtrics.com/support/survey-platform/survey-module/editing-questions/validation/#CustomValidationMessages

Thank you

And for a JavaScript option, adding the below to the OnReady section of the question’s JavaScript will disable the next button and only enable it once a selection is made for the first drilldown:

this.disableNextButton();
var that = this;
jQuery("#"+this.questionId+" select").eq(0).on('change', function() {
that.enableNextButton();
});