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.mb-3[data-argument="default_category"]{
	display:none;
}

Hide the default category field only for the places custom post type

.geodir-form-gd_place div.mb-3[data-argument="default_category"]{
	display:none;
}

Hide the default category field only for the events custom post type

.geodir-form-gd_event div.mb-3[data-argument="default_category"]{ 	
	display:none; 
}

Hide various types of near searches

/* Hide suggestions for IN search triggered by user input */

.geodir-listing-search ul.gdlmls-neighbourhood,
.geodir-listing-search ul.gdlmls-city,
.geodir-listing-search ul.gdlmls-region,
.geodir-listing-search ul.gdlmls-country {
display: none !important;
}

/* Hide API Near suggestions */

.geodir-listing-search ul.gdlmls-more{
display: none !important;

/* Hide automatic city suggestions that show when you click into the Near field */

.geodir-listing-search .list-group-item-action[data-type="city"] {
    display: none !important;
}