GeoDirectory Frequently Asked CSS customizations
These CSS customizations need to be added to your website's custom CSS. This can be done via Appearance > Customize > Custom CSS [unless your theme is taking advantage of FSE - full site editing]. Otherwise, you can add them to the style.css file of your child theme. One last alternative is to use a plugin that allows adding custom CSS such as https://wordpress.org/plugins/simple-custom-css/
How to hide the default category field from the add listing form
div.form-group[data-argument="default_category"]{ display:none; }
Hide the default category field only for the places custom post type
.geodir-form-gd_place div.form-group[data-argument="default_category"]{ display:none; }
Hide the default category field only for the events custom post type
.geodir-form-gd_event div.form-group[data-argument="default_category"]{ display:none; }