How can I make an HR Help Desk Category field required?

Summary:

Our HR Help Desk automatic (OmniChannel) routing rules are all based on the Category selected when submitting a request. In order to ensure a Category is chosen, we would like to make the field required.

Content (please ensure you mask any confidential information):

We have followed steps at https://docs.oracle.com/en/cloud/saas/fusion-service/farhd/configure-the-hr-help-desk-ui-using-application-composer.html#s20060818 in order to customize the Help Desk UI using Application Composer. Beyond the steps on that page, we have ensured that Category is listed as "required" within the "Fields" folder under "Service Request" in Application Composer. Despite this, the "Pages" folder does not allow "Category" to be selected for the typical dropdown for it to be required.